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 $119.38   11.297%   $132.8664   $132.87   $132.85   $132.90  
  Purchase #2 $209.62   12.581%   $235.9923   $235.99   $236.00   $236.00  
  Purchase #3 $147.56   7.533%   $158.6757   $158.68   $158.70   $158.70  
  Purchase #4 $168.62   7.754%   $181.6948   $181.69   $181.70   $181.70  
  Purchase #5 $226.52   7.353%   $243.176   $243.18   $243.20   $243.20  
  Purchase #6 $194.98   10.410%   $215.2774   $215.28   $215.30   $215.30  
  Purchase #7 $78.37   11.624%   $87.4797   $87.48   $87.50   $87.50  
  7 purchase totals = $1,145.05       $1,255.1623   $1,255.17   $1,255.25   $1,255.30