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 $23.51   5.687%   $24.847   $24.85   $24.85   $24.80  
  Purchase #2 $204.54   5.727%   $216.254   $216.25   $216.25   $216.30  
  Purchase #3 $7.34   4.224%   $7.65   $7.65   $7.65   $7.70  
  Purchase #4 $232.27   11.580%   $259.1669   $259.17   $259.15   $259.20  
  Purchase #5 $162.82   9.535%   $178.3449   $178.34   $178.35   $178.30  
  Purchase #6 $110.40   13.838%   $125.6772   $125.68   $125.70   $125.70  
  Purchase #7 $145.36   7.705%   $156.56   $156.56   $156.55   $156.60  
  7 purchase totals = $886.24       $968.5000   $968.50   $968.50   $968.60