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 $67.54   10.554%   $74.6682   $74.67   $74.65   $74.70  
  Purchase #2 $214.98   9.672%   $235.7729   $235.77   $235.75   $235.80  
  Purchase #3 $68.52   3.453%   $70.886   $70.89   $70.90   $70.90  
  Purchase #4 $34.89   8.614%   $37.8954   $37.90   $37.90   $37.90  
  Purchase #5 $102.88   9.133%   $112.276   $112.28   $112.30   $112.30  
  Purchase #6 $231.72   13.153%   $262.1981   $262.20   $262.20   $262.20  
  Purchase #7 $110.36   11.602%   $123.164   $123.16   $123.15   $123.20  
  7 purchase totals = $830.89       $916.8606   $916.87   $916.85   $917.00