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 $188.52   9.721%   $206.846   $206.85   $206.85   $206.80  
  Purchase #2 $23.26   8.191%   $25.1652   $25.17   $25.15   $25.20  
  Purchase #3 $48.73   11.574%   $54.37   $54.37   $54.35   $54.40  
  Purchase #4 $204.92   9.575%   $224.5411   $224.54   $224.55   $224.50  
  Purchase #5 $132.53   13.729%   $150.725   $150.73   $150.75   $150.70  
  Purchase #6 $220.71   11.539%   $246.1777   $246.18   $246.20   $246.20  
  Purchase #7 $228.56   4.635%   $239.1538   $239.15   $239.15   $239.20  
  7 purchase totals = $1,047.23       $1,146.9788   $1,146.99   $1,147.00   $1,147.00