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 $23.94   5.687%   $25.3015   $25.30   $25.30   $25.30  
  Purchase #2 $216.30   3.263%   $223.3579   $223.36   $223.35   $223.40  
  Purchase #3 $56.92   6.323%   $60.5191   $60.52   $60.50   $60.50  
  Purchase #4 $136.62   12.163%   $153.2371   $153.24   $153.25   $153.20  
  Purchase #5 $144.89   7.328%   $155.5075   $155.51   $155.50   $155.50  
  Purchase #6 $76.52   9.587%   $83.856   $83.86   $83.85   $83.90  
  Purchase #7 $177.78   3.740%   $184.429   $184.43   $184.45   $184.40  
  7 purchase totals = $832.97       $886.2081   $886.22   $886.20   $886.20