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 $246.99   7.706%   $266.023   $266.02   $266.00   $266.00  
  Purchase #2 $149.86   3.226%   $154.6945   $154.69   $154.70   $154.70  
  Purchase #3 $230.98   8.652%   $250.9644   $250.96   $250.95   $251.00  
  Purchase #4 $31.67   4.223%   $33.0074   $33.01   $33.00   $33.00  
  Purchase #5 $204.81   10.603%   $226.526   $226.53   $226.55   $226.50  
  Purchase #6 $225.93   12.501%   $254.1735   $254.17   $254.15   $254.20  
  Purchase #7 $203.83   6.526%   $217.1319   $217.13   $217.15   $217.10  
  7 purchase totals = $1,294.07       $1,402.5207   $1,402.51   $1,402.50   $1,402.50