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 $195.43   4.247%   $203.7299   $203.73   $203.75   $203.70  
  Purchase #2 $125.91   12.352%   $141.4624   $141.46   $141.45   $141.50  
  Purchase #3 $113.45   10.156%   $124.972   $124.97   $124.95   $125.00  
  Purchase #4 $183.46   5.431%   $193.4237   $193.42   $193.40   $193.40  
  Purchase #5 $88.29   10.141%   $97.2435   $97.24   $97.25   $97.20  
  Purchase #6 $34.47   13.469%   $39.1128   $39.11   $39.10   $39.10  
  Purchase #7 $230.59   10.538%   $254.8896   $254.89   $254.90   $254.90  
  7 purchase totals = $971.60       $1,054.8339   $1,054.82   $1,054.80   $1,054.80