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 $76.94   13.478%   $87.31   $87.31   $87.30   $87.30  
  Purchase #2 $150.44   10.159%   $165.7232   $165.72   $165.70   $165.70  
  Purchase #3 $105.82   9.114%   $115.4644   $115.46   $115.45   $115.50  
  Purchase #4 $60.55   6.782%   $64.6565   $64.66   $64.65   $64.70  
  Purchase #5 $22.81   9.343%   $24.9411   $24.94   $24.95   $24.90  
  Purchase #6 $201.45   3.393%   $208.2852   $208.29   $208.30   $208.30  
  Purchase #7 $151.93   3.498%   $157.2445   $157.24   $157.25   $157.20  
  7 purchase totals = $769.94       $823.6249   $823.62   $823.60   $823.60