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 $237.71   11.178%   $264.2812   $264.28   $264.30   $264.30  
  Purchase #2 $51.88   3.480%   $53.6854   $53.69   $53.70   $53.70  
  Purchase #3 $197.43   7.127%   $211.5008   $211.50   $211.50   $211.50  
  Purchase #4 $140.36   13.361%   $159.1135   $159.11   $159.10   $159.10  
  Purchase #5 $210.51   8.580%   $228.5718   $228.57   $228.55   $228.60  
  Purchase #6 $16.49   4.255%   $17.1916   $17.19   $17.20   $17.20  
  Purchase #7 $95.94   5.623%   $101.3347   $101.33   $101.35   $101.30  
  7 purchase totals = $950.32       $1,035.6790   $1,035.67   $1,035.70   $1,035.70