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 $104.77   11.177%   $116.4801   $116.48   $116.50   $116.50  
  Purchase #2 $162.41   12.814%   $183.2212   $183.22   $183.20   $183.20  
  Purchase #3 $177.30   9.754%   $194.5938   $194.59   $194.60   $194.60  
  Purchase #4 $56.93   4.293%   $59.374   $59.37   $59.35   $59.40  
  Purchase #5 $225.68   12.685%   $254.3075   $254.31   $254.30   $254.30  
  Purchase #6 $215.55   12.248%   $241.9506   $241.95   $241.95   $242.00  
  Purchase #7 $191.74   6.576%   $204.3488   $204.35   $204.35   $204.30  
  7 purchase totals = $1,134.38       $1,254.2760   $1,254.27   $1,254.25   $1,254.30