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 $88.68   6.860%   $94.7634   $94.76   $94.75   $94.80  
  Purchase #2 $88.86   3.347%   $91.8341   $91.83   $91.85   $91.80  
  Purchase #3 $174.34   3.103%   $179.7498   $179.75   $179.75   $179.70  
  Purchase #4 $70.41   4.576%   $73.632   $73.63   $73.65   $73.60  
  Purchase #5 $93.61   13.483%   $106.2314   $106.23   $106.25   $106.20  
  Purchase #6 $150.88   9.575%   $165.3268   $165.33   $165.35   $165.30  
  Purchase #7 $142.89   4.717%   $149.6301   $149.63   $149.65   $149.60  
  7 purchase totals = $809.67       $861.1676   $861.16   $861.25   $861.00