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 $58.49   6.180%   $62.1047   $62.10   $62.10   $62.10  
  Purchase #2 $111.79   8.133%   $120.8819   $120.88   $120.90   $120.90  
  Purchase #3 $158.70   11.765%   $177.3711   $177.37   $177.35   $177.40  
  Purchase #4 $220.64   9.387%   $241.3515   $241.35   $241.35   $241.40  
  Purchase #5 $226.79   4.646%   $237.3267   $237.33   $237.35   $237.30  
  Purchase #6 $16.90   5.269%   $17.7905   $17.79   $17.80   $17.80  
  Purchase #7 $92.61   8.769%   $100.731   $100.73   $100.75   $100.70  
  7 purchase totals = $885.92       $957.5574   $957.55   $957.60   $957.60