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 $223.82   4.701%   $234.3418   $234.34   $234.35   $234.30  
  Purchase #2 $86.45   13.182%   $97.8458   $97.85   $97.85   $97.80  
  Purchase #3 $240.68   9.260%   $262.967   $262.97   $262.95   $263.00  
  Purchase #4 $140.94   10.419%   $155.6245   $155.62   $155.60   $155.60  
  Purchase #5 $123.47   10.827%   $136.8381   $136.84   $136.85   $136.80  
  Purchase #6 $121.97   5.262%   $128.3881   $128.39   $128.40   $128.40  
  Purchase #7 $18.72   5.439%   $19.7382   $19.74   $19.75   $19.70  
  7 purchase totals = $956.05       $1,035.7435   $1,035.75   $1,035.75   $1,035.60