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 $66.52   12.650%   $74.9348   $74.93   $74.95   $74.90  
  Purchase #2 $170.75   3.660%   $176.9995   $177.00   $177.00   $177.00  
  Purchase #3 $79.90   3.750%   $82.8963   $82.90   $82.90   $82.90  
  Purchase #4 $116.41   3.373%   $120.3365   $120.34   $120.35   $120.30  
  Purchase #5 $33.37   11.853%   $37.3253   $37.33   $37.35   $37.30  
  Purchase #6 $237.96   13.216%   $269.4088   $269.41   $269.40   $269.40  
  Purchase #7 $244.26   11.522%   $272.4036   $272.40   $272.40   $272.40  
  7 purchase totals = $949.17       $1,034.3048   $1,034.31   $1,034.35   $1,034.20