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 $227.73   8.647%   $247.4218   $247.42   $247.40   $247.40  
  Purchase #2 $214.84   3.637%   $222.6537   $222.65   $222.65   $222.70  
  Purchase #3 $161.81   3.533%   $167.5267   $167.53   $167.55   $167.50  
  Purchase #4 $144.67   4.147%   $150.6695   $150.67   $150.65   $150.70  
  Purchase #5 $106.99   3.605%   $110.847   $110.85   $110.85   $110.80  
  Purchase #6 $215.82   10.493%   $238.466   $238.47   $238.45   $238.50  
  Purchase #7 $121.78   5.431%   $128.3939   $128.39   $128.40   $128.40  
  7 purchase totals = $1,193.64       $1,265.9786   $1,265.98   $1,265.95   $1,266.00