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 $33.61   11.122%   $37.3481   $37.35   $37.35   $37.30  
  Purchase #2 $247.29   7.646%   $266.1978   $266.20   $266.20   $266.20  
  Purchase #3 $76.33   5.362%   $80.4228   $80.42   $80.40   $80.40  
  Purchase #4 $96.96   3.843%   $100.6862   $100.69   $100.70   $100.70  
  Purchase #5 $242.66   11.861%   $271.4419   $271.44   $271.45   $271.40  
  Purchase #6 $26.96   4.670%   $28.219   $28.22   $28.20   $28.20  
  Purchase #7 $87.79   5.590%   $92.6975   $92.70   $92.70   $92.70  
  7 purchase totals = $811.60       $877.0133   $877.02   $877.00   $876.90