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 $191.67   13.484%   $217.5148   $217.51   $217.50   $217.50  
  Purchase #2 $39.98   13.272%   $45.2861   $45.29   $45.30   $45.30  
  Purchase #3 $69.58   7.517%   $74.8103   $74.81   $74.80   $74.80  
  Purchase #4 $167.85   7.561%   $180.5411   $180.54   $180.55   $180.50  
  Purchase #5 $207.29   8.296%   $224.4868   $224.49   $224.50   $224.50  
  Purchase #6 $199.57   8.606%   $216.745   $216.75   $216.75   $216.70  
  Purchase #7 $248.87   6.292%   $264.5289   $264.53   $264.55   $264.50  
  7 purchase totals = $1,124.81       $1,223.9130   $1,223.92   $1,223.95   $1,223.80