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 $216.74   13.606%   $246.2296   $246.23   $246.25   $246.20  
  Purchase #2 $229.28   5.673%   $242.2871   $242.29   $242.30   $242.30  
  Purchase #3 $87.81   7.381%   $94.2913   $94.29   $94.30   $94.30  
  Purchase #4 $71.65   4.408%   $74.8083   $74.81   $74.80   $74.80  
  Purchase #5 $240.65   3.243%   $248.4543   $248.45   $248.45   $248.50  
  Purchase #6 $246.86   4.298%   $257.47   $257.47   $257.45   $257.50  
  Purchase #7 $35.73   6.424%   $38.0253   $38.03   $38.05   $38.00  
  7 purchase totals = $1,128.72       $1,201.5659   $1,201.57   $1,201.60   $1,201.60