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 $49.73   6.714%   $53.0689   $53.07   $53.05   $53.10  
  Purchase #2 $96.98   10.262%   $106.9321   $106.93   $106.95   $106.90  
  Purchase #3 $92.53   4.715%   $96.8928   $96.89   $96.90   $96.90  
  Purchase #4 $219.43   3.128%   $226.2938   $226.29   $226.30   $226.30  
  Purchase #5 $239.82   10.638%   $265.3321   $265.33   $265.35   $265.30  
  Purchase #6 $89.97   7.628%   $96.8329   $96.83   $96.85   $96.80  
  Purchase #7 $97.94   10.525%   $108.2482   $108.25   $108.25   $108.20  
  7 purchase totals = $886.40       $953.6008   $953.59   $953.65   $953.50