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 $182.95   4.818%   $191.7645   $191.76   $191.75   $191.80  
  Purchase #2 $219.87   9.519%   $240.7994   $240.80   $240.80   $240.80  
  Purchase #3 $250.27   5.476%   $263.9748   $263.97   $263.95   $264.00  
  Purchase #4 $156.27   8.378%   $169.3623   $169.36   $169.35   $169.40  
  Purchase #5 $181.94   12.266%   $204.2568   $204.26   $204.25   $204.30  
  Purchase #6 $161.26   6.571%   $171.8564   $171.86   $171.85   $171.90  
  Purchase #7 $124.86   5.546%   $131.7847   $131.78   $131.80   $131.80  
  7 purchase totals = $1,277.42       $1,373.7989   $1,373.79   $1,373.75   $1,374.00