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 $70.99   10.663%   $78.5597   $78.56   $78.55   $78.60  
  Purchase #2 $229.35   10.458%   $253.3354   $253.34   $253.35   $253.30  
  Purchase #3 $93.51   11.166%   $103.9513   $103.95   $103.95   $104.00  
  Purchase #4 $171.75   8.451%   $186.2646   $186.26   $186.25   $186.30  
  Purchase #5 $159.79   6.407%   $170.0277   $170.03   $170.05   $170.00  
  Purchase #6 $235.58   10.466%   $260.2358   $260.24   $260.25   $260.20  
  Purchase #7 $167.87   11.750%   $187.5947   $187.59   $187.60   $187.60  
  7 purchase totals = $1,128.84       $1,239.9692   $1,239.97   $1,240.00   $1,240.00