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 $93.84   8.671%   $101.9769   $101.98   $102.00   $102.00  
  Purchase #2 $171.63   11.697%   $191.7056   $191.71   $191.70   $191.70  
  Purchase #3 $227.94   8.180%   $246.5855   $246.59   $246.60   $246.60  
  Purchase #4 $118.45   6.853%   $126.5674   $126.57   $126.55   $126.60  
  Purchase #5 $195.78   6.773%   $209.0402   $209.04   $209.05   $209.00  
  Purchase #6 $164.57   12.376%   $184.9372   $184.94   $184.95   $184.90  
  Purchase #7 $78.51   12.737%   $88.5098   $88.51   $88.50   $88.50  
  7 purchase totals = $1,050.72       $1,149.3226   $1,149.34   $1,149.35   $1,149.30