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 $141.37   11.653%   $157.8438   $157.84   $157.85   $157.80  
  Purchase #2 $173.62   8.427%   $188.251   $188.25   $188.25   $188.30  
  Purchase #3 $158.79   6.514%   $169.1336   $169.13   $169.15   $169.10  
  Purchase #4 $191.85   8.179%   $207.5414   $207.54   $207.55   $207.50  
  Purchase #5 $13.77   11.561%   $15.3619   $15.36   $15.35   $15.40  
  Purchase #6 $48.50   11.266%   $53.964   $53.96   $53.95   $54.00  
  Purchase #7 $238.27   6.611%   $254.022   $254.02   $254.00   $254.00  
  7 purchase totals = $966.17       $1,046.1177   $1,046.10   $1,046.10   $1,046.10