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 $92.72   9.559%   $101.5831   $101.58   $101.60   $101.60  
  Purchase #2 $101.86   7.664%   $109.6666   $109.67   $109.65   $109.70  
  Purchase #3 $18.53   5.553%   $19.559   $19.56   $19.55   $19.60  
  Purchase #4 $24.89   8.809%   $27.0826   $27.08   $27.10   $27.10  
  Purchase #5 $113.53   3.600%   $117.6171   $117.62   $117.60   $117.60  
  Purchase #6 $19.58   10.221%   $21.5813   $21.58   $21.60   $21.60  
  Purchase #7 $33.65   8.702%   $36.5782   $36.58   $36.60   $36.60  
  7 purchase totals = $404.76       $433.6679   $433.67   $433.70   $433.80