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 $190.76   4.561%   $199.4606   $199.46   $199.45   $199.50  
  Purchase #2 $40.42   8.631%   $43.9087   $43.91   $43.90   $43.90  
  Purchase #3 $207.37   12.346%   $232.9719   $232.97   $232.95   $233.00  
  Purchase #4 $195.62   4.112%   $203.6639   $203.66   $203.65   $203.70  
  Purchase #5 $242.90   5.747%   $256.8595   $256.86   $256.85   $256.90  
  Purchase #6 $94.84   12.726%   $106.9093   $106.91   $106.90   $106.90  
  Purchase #7 $8.30   9.854%   $9.1179   $9.12   $9.10   $9.10  
  7 purchase totals = $980.21       $1,052.8918   $1,052.89   $1,052.80   $1,053.00