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 $183.48   12.117%   $205.7123   $205.71   $205.70   $205.70  
  Purchase #2 $209.95   13.501%   $238.2953   $238.30   $238.30   $238.30  
  Purchase #3 $124.35   13.870%   $141.5973   $141.60   $141.60   $141.60  
  Purchase #4 $249.97   6.358%   $265.8631   $265.86   $265.85   $265.90  
  Purchase #5 $110.39   8.794%   $120.0977   $120.10   $120.10   $120.10  
  Purchase #6 $159.68   13.555%   $181.3246   $181.32   $181.30   $181.30  
  Purchase #7 $78.38   4.742%   $82.0968   $82.10   $82.10   $82.10  
  7 purchase totals = $1,116.20       $1,234.9871   $1,234.99   $1,234.95   $1,235.00