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 $188.27   8.863%   $204.9564   $204.96   $204.95   $205.00  
  Purchase #2 $165.57   9.297%   $180.963   $180.96   $180.95   $181.00  
  Purchase #3 $229.84   8.589%   $249.581   $249.58   $249.60   $249.60  
  Purchase #4 $118.86   7.783%   $128.1109   $128.11   $128.10   $128.10  
  Purchase #5 $82.31   8.595%   $89.3845   $89.38   $89.40   $89.40  
  Purchase #6 $24.49   9.565%   $26.8325   $26.83   $26.85   $26.80  
  Purchase #7 $107.94   9.330%   $118.0108   $118.01   $118.00   $118.00  
  7 purchase totals = $917.28       $997.8391   $997.83   $997.85   $997.90