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 $194.67   6.458%   $207.2418   $207.24   $207.25   $207.20  
  Purchase #2 $62.27   8.581%   $67.6134   $67.61   $67.60   $67.60  
  Purchase #3 $138.34   11.299%   $153.971   $153.97   $153.95   $154.00  
  Purchase #4 $241.48   4.485%   $252.3104   $252.31   $252.30   $252.30  
  Purchase #5 $163.45   7.304%   $175.3884   $175.39   $175.40   $175.40  
  Purchase #6 $26.42   7.107%   $28.2977   $28.30   $28.30   $28.30  
  Purchase #7 $187.98   9.869%   $206.5317   $206.53   $206.55   $206.50  
  7 purchase totals = $1,014.61       $1,091.3544   $1,091.35   $1,091.35   $1,091.30