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 $189.49   7.868%   $204.3991   $204.40   $204.40   $204.40  
  Purchase #2 $169.41   11.138%   $188.2789   $188.28   $188.30   $188.30  
  Purchase #3 $213.67   10.217%   $235.5007   $235.50   $235.50   $235.50  
  Purchase #4 $137.64   10.319%   $151.8431   $151.84   $151.85   $151.80  
  Purchase #5 $230.59   13.802%   $262.416   $262.42   $262.40   $262.40  
  Purchase #6 $61.38   3.420%   $63.4792   $63.48   $63.50   $63.50  
  Purchase #7 $150.44   13.460%   $170.6892   $170.69   $170.70   $170.70  
  7 purchase totals = $1,152.62       $1,276.6062   $1,276.61   $1,276.65   $1,276.60