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 $84.69   12.602%   $95.3626   $95.36   $95.35   $95.40  
  Purchase #2 $53.48   8.465%   $58.0071   $58.01   $58.00   $58.00  
  Purchase #3 $209.31   5.418%   $220.6504   $220.65   $220.65   $220.70  
  Purchase #4 $113.90   4.850%   $119.4242   $119.42   $119.40   $119.40  
  Purchase #5 $89.73   12.240%   $100.713   $100.71   $100.70   $100.70  
  Purchase #6 $168.70   6.467%   $179.6098   $179.61   $179.60   $179.60  
  Purchase #7 $230.48   6.849%   $246.2656   $246.27   $246.25   $246.30  
  7 purchase totals = $950.29       $1,020.0327   $1,020.03   $1,019.95   $1,020.10