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 $189.66   8.273%   $205.3506   $205.35   $205.35   $205.40  
  Purchase #2 $88.57   6.540%   $94.3625   $94.36   $94.35   $94.40  
  Purchase #3 $169.68   4.694%   $177.6448   $177.64   $177.65   $177.60  
  Purchase #4 $49.45   13.361%   $56.057   $56.06   $56.05   $56.10  
  Purchase #5 $181.76   4.717%   $190.3336   $190.33   $190.35   $190.30  
  Purchase #6 $138.92   8.703%   $151.0102   $151.01   $151.00   $151.00  
  Purchase #7 $138.34   5.802%   $146.3665   $146.37   $146.35   $146.40  
  7 purchase totals = $956.38       $1,021.1252   $1,021.12   $1,021.10   $1,021.20