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 $42.38   11.563%   $47.2804   $47.28   $47.30   $47.30  
  Purchase #2 $128.49   4.123%   $133.7876   $133.79   $133.80   $133.80  
  Purchase #3 $8.41   11.629%   $9.388   $9.39   $9.40   $9.40  
  Purchase #4 $156.47   8.333%   $169.5086   $169.51   $169.50   $169.50  
  Purchase #5 $54.52   7.113%   $58.398   $58.40   $58.40   $58.40  
  Purchase #6 $96.65   11.328%   $107.5985   $107.60   $107.60   $107.60  
  Purchase #7 $202.34   6.763%   $216.0243   $216.02   $216.00   $216.00  
  7 purchase totals = $689.26       $741.9854   $741.99   $742.00   $742.00