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 $93.44   3.196%   $96.4263   $96.43   $96.45   $96.40  
  Purchase #2 $202.86   11.370%   $225.9252   $225.93   $225.95   $225.90  
  Purchase #3 $179.86   5.827%   $190.3404   $190.34   $190.35   $190.30  
  Purchase #4 $117.79   13.692%   $133.9178   $133.92   $133.90   $133.90  
  Purchase #5 $22.88   8.102%   $24.7337   $24.73   $24.75   $24.70  
  Purchase #6 $11.61   9.765%   $12.7437   $12.74   $12.75   $12.70  
  Purchase #7 $26.93   13.834%   $30.6555   $30.66   $30.65   $30.70  
  7 purchase totals = $655.37       $714.7426   $714.75   $714.80   $714.60