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 $181.27   13.744%   $206.1837   $206.18   $206.20   $206.20  
  Purchase #2 $40.80   6.449%   $43.4312   $43.43   $43.45   $43.40  
  Purchase #3 $122.46   13.277%   $138.719   $138.72   $138.70   $138.70  
  Purchase #4 $143.66   3.719%   $149.0027   $149.00   $149.00   $149.00  
  Purchase #5 $5.55   10.828%   $6.151   $6.15   $6.15   $6.20  
  Purchase #6 $209.57   5.537%   $221.1739   $221.17   $221.15   $221.20  
  Purchase #7 $230.70   13.708%   $262.3244   $262.32   $262.30   $262.30  
  7 purchase totals = $934.01       $1,026.9859   $1,026.97   $1,026.95   $1,027.00