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 $63.34   8.106%   $68.4743   $68.47   $68.45   $68.50  
  Purchase #2 $171.94   13.635%   $195.384   $195.38   $195.40   $195.40  
  Purchase #3 $53.51   12.428%   $60.1602   $60.16   $60.15   $60.20  
  Purchase #4 $199.76   10.813%   $221.36   $221.36   $221.35   $221.40  
  Purchase #5 $78.93   13.761%   $89.7916   $89.79   $89.80   $89.80  
  Purchase #6 $229.99   11.306%   $255.9927   $255.99   $256.00   $256.00  
  Purchase #7 $141.28   8.120%   $152.7519   $152.75   $152.75   $152.80  
  7 purchase totals = $938.75       $1,043.9147   $1,043.90   $1,043.90   $1,044.10