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 $112.49   11.784%   $125.7458   $125.75   $125.75   $125.70  
  Purchase #2 $70.91   7.675%   $76.3523   $76.35   $76.35   $76.40  
  Purchase #3 $149.32   7.812%   $160.9849   $160.98   $161.00   $161.00  
  Purchase #4 $26.52   3.849%   $27.5408   $27.54   $27.55   $27.50  
  Purchase #5 $172.46   10.214%   $190.0751   $190.08   $190.10   $190.10  
  Purchase #6 $218.40   10.295%   $240.8843   $240.88   $240.90   $240.90  
  Purchase #7 $56.45   13.632%   $64.1453   $64.15   $64.15   $64.10  
  7 purchase totals = $806.55       $885.7285   $885.73   $885.80   $885.70