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 $94.58   12.481%   $106.3845   $106.38   $106.40   $106.40  
  Purchase #2 $223.74   4.124%   $232.967   $232.97   $232.95   $233.00  
  Purchase #3 $11.37   11.607%   $12.6897   $12.69   $12.70   $12.70  
  Purchase #4 $163.85   8.666%   $178.0492   $178.05   $178.05   $178.00  
  Purchase #5 $62.89   9.167%   $68.6551   $68.66   $68.65   $68.70  
  Purchase #6 $154.74   11.268%   $172.1761   $172.18   $172.20   $172.20  
  Purchase #7 $94.54   12.216%   $106.089   $106.09   $106.10   $106.10  
  7 purchase totals = $805.71       $877.0106   $877.02   $877.05   $877.10