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 $235.38   12.286%   $264.2988   $264.30   $264.30   $264.30  
  Purchase #2 $220.76   6.615%   $235.3633   $235.36   $235.35   $235.40  
  Purchase #3 $237.46   13.531%   $269.5907   $269.59   $269.60   $269.60  
  Purchase #4 $58.54   3.417%   $60.5403   $60.54   $60.55   $60.50  
  Purchase #5 $57.77   11.266%   $64.2784   $64.28   $64.30   $64.30  
  Purchase #6 $224.60   9.157%   $245.1666   $245.17   $245.15   $245.20  
  Purchase #7 $211.46   7.631%   $227.5965   $227.60   $227.60   $227.60  
  7 purchase totals = $1,245.97       $1,366.8346   $1,366.84   $1,366.85   $1,366.90