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 $68.40   10.461%   $75.5553   $75.56   $75.55   $75.60  
  Purchase #2 $191.26   8.284%   $207.104   $207.10   $207.10   $207.10  
  Purchase #3 $36.59   12.778%   $41.2655   $41.27   $41.25   $41.30  
  Purchase #4 $136.99   3.693%   $142.049   $142.05   $142.05   $142.00  
  Purchase #5 $144.98   12.426%   $162.9952   $163.00   $163.00   $163.00  
  Purchase #6 $185.55   10.179%   $204.4371   $204.44   $204.45   $204.40  
  Purchase #7 $170.49   5.246%   $179.4339   $179.43   $179.45   $179.40  
  7 purchase totals = $934.26       $1,012.8400   $1,012.85   $1,012.85   $1,012.80