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 $92.26   10.725%   $102.1549   $102.15   $102.15   $102.20  
  Purchase #2 $46.65   4.825%   $48.9009   $48.90   $48.90   $48.90  
  Purchase #3 $205.98   6.162%   $218.6725   $218.67   $218.65   $218.70  
  Purchase #4 $55.45   3.830%   $57.5737   $57.57   $57.55   $57.60  
  Purchase #5 $200.60   11.580%   $223.8295   $223.83   $223.85   $223.80  
  Purchase #6 $183.55   4.111%   $191.0957   $191.10   $191.10   $191.10  
  Purchase #7 $213.84   10.555%   $236.4108   $236.41   $236.40   $236.40  
  7 purchase totals = $998.33       $1,078.6380   $1,078.63   $1,078.60   $1,078.70