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 $58.39   5.771%   $61.7597   $61.76   $61.75   $61.80  
  Purchase #2 $199.45   9.803%   $219.0021   $219.00   $219.00   $219.00  
  Purchase #3 $248.77   5.470%   $262.3777   $262.38   $262.40   $262.40  
  Purchase #4 $233.27   9.729%   $255.9648   $255.96   $255.95   $256.00  
  Purchase #5 $176.52   4.451%   $184.3769   $184.38   $184.40   $184.40  
  Purchase #6 $220.63   5.397%   $232.5374   $232.54   $232.55   $232.50  
  Purchase #7 $121.42   9.529%   $132.9901   $132.99   $133.00   $133.00  
  7 purchase totals = $1,258.45       $1,349.0087   $1,349.01   $1,349.05   $1,349.10