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 $191.92   13.414%   $217.6641   $217.66   $217.65   $217.70  
  Purchase #2 $64.96   3.158%   $67.0114   $67.01   $67.00   $67.00  
  Purchase #3 $134.89   5.434%   $142.2199   $142.22   $142.20   $142.20  
  Purchase #4 $23.98   13.469%   $27.2099   $27.21   $27.20   $27.20  
  Purchase #5 $147.29   3.550%   $152.5188   $152.52   $152.50   $152.50  
  Purchase #6 $170.78   13.586%   $193.9822   $193.98   $194.00   $194.00  
  Purchase #7 $131.70   11.327%   $146.6177   $146.62   $146.60   $146.60  
  7 purchase totals = $865.52       $947.2240   $947.22   $947.15   $947.20