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 $144.44   3.772%   $149.8883   $149.89   $149.90   $149.90  
  Purchase #2 $234.43   6.829%   $250.4392   $250.44   $250.45   $250.40  
  Purchase #3 $42.86   6.410%   $45.6073   $45.61   $45.60   $45.60  
  Purchase #4 $15.86   5.336%   $16.7063   $16.71   $16.70   $16.70  
  Purchase #5 $167.67   8.352%   $181.6738   $181.67   $181.65   $181.70  
  Purchase #6 $10.55   13.726%   $11.9981   $12.00   $12.00   $12.00  
  Purchase #7 $161.56   7.598%   $173.8353   $173.84   $173.85   $173.80  
  7 purchase totals = $777.37       $830.1483   $830.16   $830.15   $830.10