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 $239.51   10.638%   $264.9891   $264.99   $265.00   $265.00  
  Purchase #2 $80.40   7.665%   $86.5627   $86.56   $86.55   $86.60  
  Purchase #3 $130.62   5.811%   $138.2103   $138.21   $138.20   $138.20  
  Purchase #4 $179.32   11.485%   $199.9149   $199.91   $199.90   $199.90  
  Purchase #5 $94.44   12.348%   $106.1015   $106.10   $106.10   $106.10  
  Purchase #6 $141.87   6.153%   $150.5993   $150.60   $150.60   $150.60  
  Purchase #7 $180.87   13.208%   $204.7593   $204.76   $204.75   $204.80  
  7 purchase totals = $1,047.03       $1,151.1371   $1,151.13   $1,151.10   $1,151.20