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 $197.57   3.129%   $203.752   $203.75   $203.75   $203.80  
  Purchase #2 $82.96   10.818%   $91.9346   $91.93   $91.95   $91.90  
  Purchase #3 $17.97   3.736%   $18.6414   $18.64   $18.65   $18.60  
  Purchase #4 $195.55   9.802%   $214.7178   $214.72   $214.70   $214.70  
  Purchase #5 $215.97   11.587%   $240.9944   $240.99   $241.00   $241.00  
  Purchase #6 $85.35   5.574%   $90.1074   $90.11   $90.10   $90.10  
  Purchase #7 $12.75   9.195%   $13.9224   $13.92   $13.90   $13.90  
  7 purchase totals = $808.12       $874.0700   $874.06   $874.05   $874.00