Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $181.66   12.157%   $203.7444   $203.74   $203.75   $203.70  
  Purchase #2 $232.92   5.642%   $246.0613   $246.06   $246.05   $246.10  
  Purchase #3 $100.69   6.849%   $107.5863   $107.59   $107.60   $107.60  
  Purchase #4 $123.66   10.592%   $136.7581   $136.76   $136.75   $136.80  
  Purchase #5 $193.35   6.518%   $205.9526   $205.95   $205.95   $206.00  
  Purchase #6 $246.83   12.634%   $278.0145   $278.01   $278.00   $278.00  
  Purchase #7 $163.26   11.723%   $182.399   $182.40   $182.40   $182.40  
  7 purchase totals = $1,242.37       $1,360.5162   $1,360.51   $1,360.50   $1,360.60