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 $46.48   4.498%   $48.5707   $48.57   $48.55   $48.60  
  Purchase #2 $197.31   11.184%   $219.3772   $219.38   $219.40   $219.40  
  Purchase #3 $225.25   11.103%   $250.2595   $250.26   $250.25   $250.30  
  Purchase #4 $223.38   12.648%   $251.6331   $251.63   $251.65   $251.60  
  Purchase #5 $32.85   6.368%   $34.9419   $34.94   $34.95   $34.90  
  Purchase #6 $204.71   4.270%   $213.4511   $213.45   $213.45   $213.50  
  Purchase #7 $184.63   8.507%   $200.3365   $200.34   $200.35   $200.30  
  7 purchase totals = $1,114.61       $1,218.5700   $1,218.57   $1,218.60   $1,218.60