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 $60.47   12.750%   $68.1799   $68.18   $68.20   $68.20  
  Purchase #2 $227.76   11.453%   $253.8454   $253.85   $253.85   $253.80  
  Purchase #3 $116.48   4.794%   $122.0641   $122.06   $122.05   $122.10  
  Purchase #4 $19.72   8.171%   $21.3313   $21.33   $21.35   $21.30  
  Purchase #5 $221.84   9.680%   $243.3141   $243.31   $243.30   $243.30  
  Purchase #6 $29.84   13.743%   $33.9409   $33.94   $33.95   $33.90  
  Purchase #7 $111.45   7.260%   $119.5413   $119.54   $119.55   $119.50  
  7 purchase totals = $787.56       $862.2170   $862.21   $862.25   $862.10