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 $118.27   11.457%   $131.8202   $131.82   $131.80   $131.80  
  Purchase #2 $15.35   6.154%   $16.2946   $16.29   $16.30   $16.30  
  Purchase #3 $47.93   5.805%   $50.7123   $50.71   $50.70   $50.70  
  Purchase #4 $178.88   8.437%   $193.9721   $193.97   $193.95   $194.00  
  Purchase #5 $207.41   8.729%   $225.5148   $225.51   $225.50   $225.50  
  Purchase #6 $81.45   4.707%   $85.2839   $85.28   $85.30   $85.30  
  Purchase #7 $225.32   5.284%   $237.2259   $237.23   $237.25   $237.20  
  7 purchase totals = $874.61       $940.8238   $940.81   $940.80   $940.80