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 $243.63   8.249%   $263.727   $263.73   $263.75   $263.70  
  Purchase #2 $92.72   5.812%   $98.1089   $98.11   $98.10   $98.10  
  Purchase #3 $56.82   11.432%   $63.3157   $63.32   $63.30   $63.30  
  Purchase #4 $113.57   12.539%   $127.8105   $127.81   $127.80   $127.80  
  Purchase #5 $191.32   5.562%   $201.9612   $201.96   $201.95   $202.00  
  Purchase #6 $16.49   11.338%   $18.3596   $18.36   $18.35   $18.40  
  Purchase #7 $170.75   8.245%   $184.8283   $184.83   $184.85   $184.80  
  7 purchase totals = $885.30       $958.1112   $958.12   $958.10   $958.10