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 $54.86   6.527%   $58.4407   $58.44   $58.45   $58.40  
  Purchase #2 $130.72   13.432%   $148.2783   $148.28   $148.30   $148.30  
  Purchase #3 $170.35   5.268%   $179.324   $179.32   $179.30   $179.30  
  Purchase #4 $243.73   5.421%   $256.9426   $256.94   $256.95   $256.90  
  Purchase #5 $41.64   6.786%   $44.4657   $44.47   $44.45   $44.50  
  Purchase #6 $199.51   3.486%   $206.4649   $206.46   $206.45   $206.50  
  Purchase #7 $149.30   10.399%   $164.8257   $164.83   $164.85   $164.80  
  7 purchase totals = $990.11       $1,058.7419   $1,058.74   $1,058.75   $1,058.70