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 $154.33   11.196%   $171.6088   $171.61   $171.60   $171.60  
  Purchase #2 $87.87   4.660%   $91.9647   $91.96   $91.95   $92.00  
  Purchase #3 $247.55   11.464%   $275.9291   $275.93   $275.95   $275.90  
  Purchase #4 $116.75   11.445%   $130.112   $130.11   $130.10   $130.10  
  Purchase #5 $51.67   12.857%   $58.3132   $58.31   $58.30   $58.30  
  Purchase #6 $147.50   5.191%   $155.1567   $155.16   $155.15   $155.20  
  Purchase #7 $150.84   6.739%   $161.0051   $161.01   $161.00   $161.00  
  7 purchase totals = $956.51       $1,044.0896   $1,044.09   $1,044.05   $1,044.10