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 $204.86   13.138%   $231.7745   $231.77   $231.75   $231.80  
  Purchase #2 $177.49   9.399%   $194.1723   $194.17   $194.15   $194.20  
  Purchase #3 $60.67   5.740%   $64.1525   $64.15   $64.15   $64.20  
  Purchase #4 $214.89   4.229%   $223.9777   $223.98   $224.00   $224.00  
  Purchase #5 $41.75   4.597%   $43.6692   $43.67   $43.65   $43.70  
  Purchase #6 $108.34   5.738%   $114.5565   $114.56   $114.55   $114.60  
  Purchase #7 $207.43   6.321%   $220.5417   $220.54   $220.55   $220.50  
  7 purchase totals = $1,015.43       $1,092.8444   $1,092.84   $1,092.80   $1,093.00