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 $241.47   13.665%   $274.4669   $274.47   $274.45   $274.50  
  Purchase #2 $111.57   9.658%   $122.3454   $122.35   $122.35   $122.30  
  Purchase #3 $33.74   11.233%   $37.53   $37.53   $37.55   $37.50  
  Purchase #4 $213.55   7.865%   $230.3457   $230.35   $230.35   $230.30  
  Purchase #5 $27.26   5.308%   $28.707   $28.71   $28.70   $28.70  
  Purchase #6 $152.87   6.408%   $162.6659   $162.67   $162.65   $162.70  
  Purchase #7 $203.97   13.862%   $232.2443   $232.24   $232.25   $232.20  
  7 purchase totals = $984.43       $1,088.3052   $1,088.32   $1,088.30   $1,088.20