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 $248.36   9.809%   $272.7216   $272.72   $272.70   $272.70  
  Purchase #2 $71.68   8.260%   $77.6008   $77.60   $77.60   $77.60  
  Purchase #3 $101.71   11.356%   $113.2602   $113.26   $113.25   $113.30  
  Purchase #4 $174.36   4.388%   $182.0109   $182.01   $182.00   $182.00  
  Purchase #5 $129.73   4.756%   $135.9   $135.90   $135.90   $135.90  
  Purchase #6 $182.61   12.331%   $205.1276   $205.13   $205.15   $205.10  
  Purchase #7 $68.47   13.478%   $77.6984   $77.70   $77.70   $77.70  
  7 purchase totals = $976.92       $1,064.3195   $1,064.32   $1,064.30   $1,064.30