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 $9.52   7.131%   $10.1989   $10.20   $10.20   $10.20  
  Purchase #2 $139.36   7.720%   $150.1186   $150.12   $150.10   $150.10  
  Purchase #3 $122.68   12.574%   $138.1058   $138.11   $138.10   $138.10  
  Purchase #4 $65.25   10.422%   $72.0504   $72.05   $72.05   $72.10  
  Purchase #5 $159.34   11.432%   $177.5557   $177.56   $177.55   $177.60  
  Purchase #6 $105.91   13.764%   $120.4875   $120.49   $120.50   $120.50  
  Purchase #7 $143.26   9.605%   $157.0201   $157.02   $157.00   $157.00  
  7 purchase totals = $745.32       $825.5370   $825.55   $825.50   $825.60