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 $227.46   10.578%   $251.5207   $251.52   $251.50   $251.50  
  Purchase #2 $155.91   13.646%   $177.1855   $177.19   $177.20   $177.20  
  Purchase #3 $64.28   10.318%   $70.9124   $70.91   $70.90   $70.90  
  Purchase #4 $119.72   4.370%   $124.9518   $124.95   $124.95   $125.00  
  Purchase #5 $146.96   11.549%   $163.9324   $163.93   $163.95   $163.90  
  Purchase #6 $216.58   11.122%   $240.668   $240.67   $240.65   $240.70  
  Purchase #7 $51.94   12.514%   $58.4398   $58.44   $58.45   $58.40  
  7 purchase totals = $982.85       $1,087.6106   $1,087.61   $1,087.60   $1,087.60