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 $231.85   13.408%   $262.9364   $262.94   $262.95   $262.90  
  Purchase #2 $114.96   12.256%   $129.0495   $129.05   $129.05   $129.00  
  Purchase #3 $191.32   6.607%   $203.9605   $203.96   $203.95   $204.00  
  Purchase #4 $185.80   4.826%   $194.7667   $194.77   $194.75   $194.80  
  Purchase #5 $29.51   11.751%   $32.9777   $32.98   $33.00   $33.00  
  Purchase #6 $160.64   9.526%   $175.9426   $175.94   $175.95   $175.90  
  Purchase #7 $32.67   12.582%   $36.7805   $36.78   $36.80   $36.80  
  7 purchase totals = $946.75       $1,036.4139   $1,036.42   $1,036.45   $1,036.40