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 $191.42   13.183%   $216.6549   $216.65   $216.65   $216.70  
  Purchase #2 $39.67   4.815%   $41.5801   $41.58   $41.60   $41.60  
  Purchase #3 $83.45   13.805%   $94.9703   $94.97   $94.95   $95.00  
  Purchase #4 $233.47   3.537%   $241.7278   $241.73   $241.75   $241.70  
  Purchase #5 $183.27   9.340%   $200.3874   $200.39   $200.40   $200.40  
  Purchase #6 $67.28   12.183%   $75.4767   $75.48   $75.50   $75.50  
  Purchase #7 $164.78   7.683%   $177.44   $177.44   $177.45   $177.40  
  7 purchase totals = $963.34       $1,048.2372   $1,048.24   $1,048.30   $1,048.30