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 $218.70   12.467%   $245.9653   $245.97   $245.95   $246.00  
  Purchase #2 $141.60   8.509%   $153.6487   $153.65   $153.65   $153.60  
  Purchase #3 $240.26   10.351%   $265.1293   $265.13   $265.15   $265.10  
  Purchase #4 $193.67   5.361%   $204.0526   $204.05   $204.05   $204.10  
  Purchase #5 $11.50   9.235%   $12.562   $12.56   $12.55   $12.60  
  Purchase #6 $153.27   7.535%   $164.8189   $164.82   $164.80   $164.80  
  Purchase #7 $88.46   4.635%   $92.5601   $92.56   $92.55   $92.60  
  7 purchase totals = $1,047.46       $1,138.7369   $1,138.74   $1,138.70   $1,138.80