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 $67.94   12.223%   $76.2443   $76.24   $76.25   $76.20  
  Purchase #2 $53.31   7.328%   $57.2166   $57.22   $57.20   $57.20  
  Purchase #3 $225.94   9.238%   $246.8123   $246.81   $246.80   $246.80  
  Purchase #4 $129.36   5.311%   $136.2303   $136.23   $136.25   $136.20  
  Purchase #5 $236.86   6.489%   $252.2298   $252.23   $252.25   $252.20  
  Purchase #6 $136.78   11.594%   $152.6383   $152.64   $152.65   $152.60  
  Purchase #7 $103.92   13.160%   $117.5959   $117.60   $117.60   $117.60  
  7 purchase totals = $954.11       $1,038.9675   $1,038.97   $1,039.00   $1,038.80