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 $240.67   8.109%   $260.1859   $260.19   $260.20   $260.20  
  Purchase #2 $38.55   8.744%   $41.9208   $41.92   $41.90   $41.90  
  Purchase #3 $248.27   9.828%   $272.67   $272.67   $272.65   $272.70  
  Purchase #4 $121.44   3.837%   $126.0997   $126.10   $126.10   $126.10  
  Purchase #5 $123.28   13.291%   $139.6651   $139.67   $139.65   $139.70  
  Purchase #6 $247.90   8.329%   $268.5476   $268.55   $268.55   $268.50  
  Purchase #7 $198.94   11.331%   $221.4819   $221.48   $221.50   $221.50  
  7 purchase totals = $1,219.05       $1,330.5710   $1,330.58   $1,330.55   $1,330.60