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 $203.58   10.328%   $224.6057   $224.61   $224.60   $224.60  
  Purchase #2 $54.82   10.157%   $60.3881   $60.39   $60.40   $60.40  
  Purchase #3 $230.81   11.700%   $257.8148   $257.81   $257.80   $257.80  
  Purchase #4 $59.77   13.686%   $67.9501   $67.95   $67.95   $68.00  
  Purchase #5 $147.31   10.115%   $162.2104   $162.21   $162.20   $162.20  
  Purchase #6 $181.38   9.149%   $197.9745   $197.97   $197.95   $198.00  
  Purchase #7 $93.76   11.746%   $104.773   $104.77   $104.75   $104.80  
  7 purchase totals = $971.43       $1,075.7166   $1,075.71   $1,075.65   $1,075.80