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 $211.25   12.473%   $237.5992   $237.60   $237.60   $237.60  
  Purchase #2 $88.92   11.833%   $99.4419   $99.44   $99.45   $99.40  
  Purchase #3 $248.72   10.815%   $275.6191   $275.62   $275.60   $275.60  
  Purchase #4 $56.93   13.616%   $64.6816   $64.68   $64.70   $64.70  
  Purchase #5 $82.25   5.755%   $86.9835   $86.98   $87.00   $87.00  
  Purchase #6 $221.97   7.690%   $239.0395   $239.04   $239.05   $239.00  
  Purchase #7 $53.53   3.689%   $55.5047   $55.50   $55.50   $55.50  
  7 purchase totals = $963.57       $1,058.8695   $1,058.86   $1,058.90   $1,058.80