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 $146.68   13.650%   $166.7018   $166.70   $166.70   $166.70  
  Purchase #2 $14.36   6.766%   $15.3316   $15.33   $15.35   $15.30  
  Purchase #3 $119.98   12.131%   $134.5348   $134.53   $134.55   $134.50  
  Purchase #4 $74.63   10.143%   $82.1997   $82.20   $82.20   $82.20  
  Purchase #5 $231.55   6.353%   $246.2604   $246.26   $246.25   $246.30  
  Purchase #6 $156.84   6.793%   $167.4941   $167.49   $167.50   $167.50  
  Purchase #7 $196.42   13.745%   $223.4179   $223.42   $223.40   $223.40  
  7 purchase totals = $940.46       $1,035.9403   $1,035.93   $1,035.95   $1,035.90