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 $217.37   11.853%   $243.1349   $243.13   $243.15   $243.10  
  Purchase #2 $119.54   8.376%   $129.5527   $129.55   $129.55   $129.60  
  Purchase #3 $108.28   8.692%   $117.6917   $117.69   $117.70   $117.70  
  Purchase #4 $91.44   10.715%   $101.2378   $101.24   $101.25   $101.20  
  Purchase #5 $187.80   5.252%   $197.6633   $197.66   $197.65   $197.70  
  Purchase #6 $26.94   3.580%   $27.9045   $27.90   $27.90   $27.90  
  Purchase #7 $229.50   5.192%   $241.4156   $241.42   $241.40   $241.40  
  7 purchase totals = $980.87       $1,058.6005   $1,058.59   $1,058.60   $1,058.60