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 $245.32   13.251%   $277.8274   $277.83   $277.85   $277.80  
  Purchase #2 $55.31   13.478%   $62.7647   $62.76   $62.75   $62.80  
  Purchase #3 $192.71   4.516%   $201.4128   $201.41   $201.40   $201.40  
  Purchase #4 $132.51   5.153%   $139.3382   $139.34   $139.35   $139.30  
  Purchase #5 $185.98   9.351%   $203.371   $203.37   $203.35   $203.40  
  Purchase #6 $33.26   3.426%   $34.3995   $34.40   $34.40   $34.40  
  Purchase #7 $197.56   5.210%   $207.8529   $207.85   $207.85   $207.90  
  7 purchase totals = $1,042.65       $1,126.9665   $1,126.96   $1,126.95   $1,127.00