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 $183.43   9.858%   $201.5125   $201.51   $201.50   $201.50  
  Purchase #2 $224.86   4.434%   $234.8303   $234.83   $234.85   $234.80  
  Purchase #3 $88.78   6.293%   $94.3669   $94.37   $94.35   $94.40  
  Purchase #4 $159.34   6.566%   $169.8023   $169.80   $169.80   $169.80  
  Purchase #5 $161.77   13.341%   $183.3517   $183.35   $183.35   $183.40  
  Purchase #6 $202.98   6.558%   $216.2914   $216.29   $216.30   $216.30  
  Purchase #7 $106.27   10.796%   $117.7429   $117.74   $117.75   $117.70  
  7 purchase totals = $1,127.43       $1,217.8980   $1,217.89   $1,217.90   $1,217.90