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 $115.54   6.739%   $123.3262   $123.33   $123.35   $123.30  
  Purchase #2 $26.56   6.780%   $28.3608   $28.36   $28.35   $28.40  
  Purchase #3 $170.47   11.483%   $190.0451   $190.05   $190.05   $190.00  
  Purchase #4 $197.40   6.731%   $210.687   $210.69   $210.70   $210.70  
  Purchase #5 $228.95   9.545%   $250.8033   $250.80   $250.80   $250.80  
  Purchase #6 $173.99   10.464%   $192.1963   $192.20   $192.20   $192.20  
  Purchase #7 $14.72   12.522%   $16.5632   $16.56   $16.55   $16.60  
  7 purchase totals = $927.63       $1,011.9819   $1,011.99   $1,012.00   $1,012.00