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 $69.86   10.718%   $77.3476   $77.35   $77.35   $77.30  
  Purchase #2 $184.75   9.185%   $201.7193   $201.72   $201.70   $201.70  
  Purchase #3 $227.65   12.861%   $256.9281   $256.93   $256.95   $256.90  
  Purchase #4 $203.91   6.478%   $217.1193   $217.12   $217.10   $217.10  
  Purchase #5 $157.70   10.236%   $173.8422   $173.84   $173.85   $173.80  
  Purchase #6 $179.82   7.146%   $192.6699   $192.67   $192.65   $192.70  
  Purchase #7 $208.86   13.235%   $236.5026   $236.50   $236.50   $236.50  
  7 purchase totals = $1,232.55       $1,356.1290   $1,356.13   $1,356.10   $1,356.00