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 $182.65   12.548%   $205.5689   $205.57   $205.55   $205.60  
  Purchase #2 $94.92   6.165%   $100.7718   $100.77   $100.75   $100.80  
  Purchase #3 $63.95   9.226%   $69.85   $69.85   $69.85   $69.90  
  Purchase #4 $232.35   13.278%   $263.2014   $263.20   $263.20   $263.20  
  Purchase #5 $143.37   9.324%   $156.7378   $156.74   $156.75   $156.70  
  Purchase #6 $178.73   9.491%   $195.6933   $195.69   $195.70   $195.70  
  Purchase #7 $203.92   8.758%   $221.7793   $221.78   $221.80   $221.80  
  7 purchase totals = $1,099.89       $1,213.6025   $1,213.60   $1,213.60   $1,213.70