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 $118.67   7.503%   $127.5738   $127.57   $127.55   $127.60  
  Purchase #2 $87.48   12.784%   $98.6634   $98.66   $98.65   $98.70  
  Purchase #3 $48.56   11.621%   $54.2032   $54.20   $54.20   $54.20  
  Purchase #4 $75.81   10.857%   $84.0407   $84.04   $84.05   $84.00  
  Purchase #5 $195.79   12.844%   $220.9373   $220.94   $220.95   $220.90  
  Purchase #6 $132.79   5.351%   $139.8956   $139.90   $139.90   $139.90  
  Purchase #7 $31.93   10.634%   $35.3254   $35.33   $35.35   $35.30  
  7 purchase totals = $691.03       $760.6394   $760.64   $760.65   $760.60