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 $105.50   3.314%   $108.9963   $109.00   $109.00   $109.00  
  Purchase #2 $197.96   10.390%   $218.528   $218.53   $218.55   $218.50  
  Purchase #3 $235.29   11.776%   $262.9978   $263.00   $263.00   $263.00  
  Purchase #4 $104.46   5.861%   $110.5824   $110.58   $110.60   $110.60  
  Purchase #5 $13.78   8.569%   $14.9608   $14.96   $14.95   $15.00  
  Purchase #6 $120.68   4.249%   $125.8077   $125.81   $125.80   $125.80  
  Purchase #7 $28.31   4.689%   $29.6375   $29.64   $29.65   $29.60  
  7 purchase totals = $805.98       $871.5105   $871.52   $871.55   $871.50