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 $56.65   11.754%   $63.3086   $63.31   $63.30   $63.30  
  Purchase #2 $216.64   6.294%   $230.2753   $230.28   $230.30   $230.30  
  Purchase #3 $44.62   9.256%   $48.75   $48.75   $48.75   $48.80  
  Purchase #4 $88.79   13.445%   $100.7278   $100.73   $100.75   $100.70  
  Purchase #5 $181.57   11.181%   $201.8713   $201.87   $201.85   $201.90  
  Purchase #6 $215.73   6.581%   $229.9272   $229.93   $229.95   $229.90  
  Purchase #7 $168.88   9.505%   $184.932   $184.93   $184.95   $184.90  
  7 purchase totals = $972.88       $1,059.7922   $1,059.80   $1,059.85   $1,059.80