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 $215.67   13.239%   $244.2226   $244.22   $244.20   $244.20  
  Purchase #2 $20.69   9.635%   $22.6835   $22.68   $22.70   $22.70  
  Purchase #3 $48.37   12.550%   $54.4404   $54.44   $54.45   $54.40  
  Purchase #4 $202.44   13.418%   $229.6034   $229.60   $229.60   $229.60  
  Purchase #5 $85.26   13.530%   $96.7957   $96.80   $96.80   $96.80  
  Purchase #6 $191.72   11.548%   $213.8598   $213.86   $213.85   $213.90  
  Purchase #7 $174.71   4.862%   $183.2044   $183.20   $183.20   $183.20  
  7 purchase totals = $938.86       $1,044.8098   $1,044.80   $1,044.80   $1,044.80