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 $113.89   9.443%   $124.6446   $124.64   $124.65   $124.60  
  Purchase #2 $209.57   4.277%   $218.5333   $218.53   $218.55   $218.50  
  Purchase #3 $160.96   8.199%   $174.1571   $174.16   $174.15   $174.20  
  Purchase #4 $181.83   10.772%   $201.4167   $201.42   $201.40   $201.40  
  Purchase #5 $234.41   4.513%   $244.9889   $244.99   $245.00   $245.00  
  Purchase #6 $205.54   10.653%   $227.4362   $227.44   $227.45   $227.40  
  Purchase #7 $165.86   9.707%   $181.96   $181.96   $181.95   $182.00  
  7 purchase totals = $1,272.06       $1,373.1368   $1,373.14   $1,373.15   $1,373.10