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 $84.77   13.289%   $96.0351   $96.04   $96.05   $96.00  
  Purchase #2 $7.96   6.571%   $8.4831   $8.48   $8.50   $8.50  
  Purchase #3 $111.30   3.611%   $115.319   $115.32   $115.30   $115.30  
  Purchase #4 $224.60   4.288%   $234.2308   $234.23   $234.25   $234.20  
  Purchase #5 $111.28   12.498%   $125.1878   $125.19   $125.20   $125.20  
  Purchase #6 $233.71   6.764%   $249.5181   $249.52   $249.50   $249.50  
  Purchase #7 $173.93   11.543%   $194.0067   $194.01   $194.00   $194.00  
  7 purchase totals = $947.55       $1,022.7806   $1,022.79   $1,022.80   $1,022.70