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 $179.88   13.247%   $203.7087   $203.71   $203.70   $203.70  
  Purchase #2 $216.49   4.325%   $225.8532   $225.85   $225.85   $225.90  
  Purchase #3 $26.47   4.379%   $27.6291   $27.63   $27.65   $27.60  
  Purchase #4 $193.99   3.617%   $201.0066   $201.01   $201.00   $201.00  
  Purchase #5 $14.96   9.104%   $16.322   $16.32   $16.30   $16.30  
  Purchase #6 $154.37   4.313%   $161.028   $161.03   $161.05   $161.00  
  Purchase #7 $204.99   10.195%   $225.8887   $225.89   $225.90   $225.90  
  7 purchase totals = $991.15       $1,061.4363   $1,061.44   $1,061.45   $1,061.40