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 $42.55   3.438%   $44.0129   $44.01   $44.00   $44.00  
  Purchase #2 $176.38   3.728%   $182.9554   $182.96   $182.95   $183.00  
  Purchase #3 $15.92   4.186%   $16.5864   $16.59   $16.60   $16.60  
  Purchase #4 $204.44   11.661%   $228.2797   $228.28   $228.30   $228.30  
  Purchase #5 $216.95   3.471%   $224.4803   $224.48   $224.50   $224.50  
  Purchase #6 $229.42   7.811%   $247.34   $247.34   $247.35   $247.30  
  Purchase #7 $67.43   12.135%   $75.6126   $75.61   $75.60   $75.60  
  7 purchase totals = $953.09       $1,019.2673   $1,019.27   $1,019.30   $1,019.30