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 $244.98   4.573%   $256.1829   $256.18   $256.20   $256.20  
  Purchase #2 $245.29   13.172%   $277.5996   $277.60   $277.60   $277.60  
  Purchase #3 $202.31   11.217%   $225.0031   $225.00   $225.00   $225.00  
  Purchase #4 $12.78   6.381%   $13.5955   $13.60   $13.60   $13.60  
  Purchase #5 $152.53   8.810%   $165.9679   $165.97   $165.95   $166.00  
  Purchase #6 $244.90   10.200%   $269.8798   $269.88   $269.90   $269.90  
  Purchase #7 $58.43   6.334%   $62.131   $62.13   $62.15   $62.10  
  7 purchase totals = $1,161.22       $1,270.3598   $1,270.36   $1,270.40   $1,270.40