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 $161.84   13.469%   $183.6382   $183.64   $183.65   $183.60  
  Purchase #2 $31.98   6.386%   $34.0222   $34.02   $34.00   $34.00  
  Purchase #3 $154.94   10.243%   $170.8105   $170.81   $170.80   $170.80  
  Purchase #4 $59.90   3.423%   $61.9504   $61.95   $61.95   $62.00  
  Purchase #5 $184.75   12.747%   $208.3001   $208.30   $208.30   $208.30  
  Purchase #6 $138.52   10.625%   $153.2378   $153.24   $153.25   $153.20  
  Purchase #7 $126.94   11.249%   $141.2195   $141.22   $141.20   $141.20  
  7 purchase totals = $858.87       $953.1787   $953.18   $953.15   $953.10