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 $63.96   3.473%   $66.1813   $66.18   $66.20   $66.20  
  Purchase #2 $140.58   9.296%   $153.6483   $153.65   $153.65   $153.60  
  Purchase #3 $153.71   12.754%   $173.3142   $173.31   $173.30   $173.30  
  Purchase #4 $125.93   11.795%   $140.7834   $140.78   $140.80   $140.80  
  Purchase #5 $216.57   7.607%   $233.0445   $233.04   $233.05   $233.00  
  Purchase #6 $55.52   13.845%   $63.2067   $63.21   $63.20   $63.20  
  Purchase #7 $130.39   8.745%   $141.7926   $141.79   $141.80   $141.80  
  7 purchase totals = $886.66       $971.9710   $971.96   $972.00   $971.90