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 $66.49   10.274%   $73.3212   $73.32   $73.30   $73.30  
  Purchase #2 $173.95   13.429%   $197.3097   $197.31   $197.30   $197.30  
  Purchase #3 $69.54   3.368%   $71.8821   $71.88   $71.90   $71.90  
  Purchase #4 $187.53   6.197%   $199.1512   $199.15   $199.15   $199.20  
  Purchase #5 $220.50   11.714%   $246.3294   $246.33   $246.35   $246.30  
  Purchase #6 $185.44   11.403%   $206.5857   $206.59   $206.60   $206.60  
  Purchase #7 $54.84   13.131%   $62.041   $62.04   $62.05   $62.00  
  7 purchase totals = $958.29       $1,056.6203   $1,056.62   $1,056.65   $1,056.60