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 $203.69   11.448%   $227.0084   $227.01   $227.00   $227.00  
  Purchase #2 $5.55   8.149%   $6.0023   $6.00   $6.00   $6.00  
  Purchase #3 $88.82   4.114%   $92.4741   $92.47   $92.45   $92.50  
  Purchase #4 $229.43   6.546%   $244.4485   $244.45   $244.45   $244.40  
  Purchase #5 $197.81   11.694%   $220.9419   $220.94   $220.95   $220.90  
  Purchase #6 $194.81   8.575%   $211.515   $211.52   $211.50   $211.50  
  Purchase #7 $158.60   9.766%   $174.0889   $174.09   $174.10   $174.10  
  7 purchase totals = $1,078.71       $1,176.4791   $1,176.48   $1,176.45   $1,176.40