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 $45.52   13.860%   $51.8291   $51.83   $51.85   $51.80  
  Purchase #2 $124.87   10.789%   $138.3422   $138.34   $138.35   $138.30  
  Purchase #3 $211.53   8.249%   $228.9791   $228.98   $229.00   $229.00  
  Purchase #4 $22.35   3.349%   $23.0985   $23.10   $23.10   $23.10  
  Purchase #5 $12.95   11.858%   $14.4856   $14.49   $14.50   $14.50  
  Purchase #6 $207.51   12.303%   $233.04   $233.04   $233.05   $233.00  
  Purchase #7 $237.72   4.202%   $247.709   $247.71   $247.70   $247.70  
  7 purchase totals = $862.45       $937.4835   $937.49   $937.55   $937.40