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 $68.34   8.278%   $73.9972   $74.00   $74.00   $74.00  
  Purchase #2 $127.41   10.857%   $141.2429   $141.24   $141.25   $141.20  
  Purchase #3 $84.64   13.547%   $96.1062   $96.11   $96.10   $96.10  
  Purchase #4 $55.97   4.243%   $58.3448   $58.34   $58.35   $58.30  
  Purchase #5 $132.43   8.852%   $144.1527   $144.15   $144.15   $144.20  
  Purchase #6 $188.74   11.793%   $210.9981   $211.00   $211.00   $211.00  
  Purchase #7 $244.33   11.653%   $272.8018   $272.80   $272.80   $272.80  
  7 purchase totals = $901.86       $997.6437   $997.64   $997.65   $997.60