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 $218.44   13.517%   $247.9665   $247.97   $247.95   $248.00  
  Purchase #2 $62.90   4.478%   $65.7167   $65.72   $65.70   $65.70  
  Purchase #3 $159.70   10.707%   $176.7991   $176.80   $176.80   $176.80  
  Purchase #4 $246.86   9.832%   $271.1313   $271.13   $271.15   $271.10  
  Purchase #5 $202.88   12.751%   $228.7492   $228.75   $228.75   $228.70  
  Purchase #6 $231.76   11.174%   $257.6569   $257.66   $257.65   $257.70  
  Purchase #7 $150.95   10.334%   $166.5492   $166.55   $166.55   $166.50  
  7 purchase totals = $1,273.49       $1,414.5689   $1,414.58   $1,414.55   $1,414.50