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 $56.70   11.301%   $63.1077   $63.11   $63.10   $63.10  
  Purchase #2 $130.96   12.117%   $146.8284   $146.83   $146.85   $146.80  
  Purchase #3 $77.94   7.752%   $83.9819   $83.98   $84.00   $84.00  
  Purchase #4 $127.42   4.552%   $133.2202   $133.22   $133.20   $133.20  
  Purchase #5 $217.42   9.761%   $238.6424   $238.64   $238.65   $238.60  
  Purchase #6 $196.27   11.168%   $218.1894   $218.19   $218.20   $218.20  
  Purchase #7 $164.64   10.242%   $181.5024   $181.50   $181.50   $181.50  
  7 purchase totals = $971.35       $1,065.4724   $1,065.47   $1,065.50   $1,065.40