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 $204.47   12.260%   $229.538   $229.54   $229.55   $229.50  
  Purchase #2 $236.65   13.432%   $268.4368   $268.44   $268.45   $268.40  
  Purchase #3 $106.67   12.537%   $120.0432   $120.04   $120.05   $120.00  
  Purchase #4 $49.65   4.499%   $51.8838   $51.88   $51.90   $51.90  
  Purchase #5 $98.89   6.219%   $105.04   $105.04   $105.05   $105.00  
  Purchase #6 $214.69   4.160%   $223.6211   $223.62   $223.60   $223.60  
  Purchase #7 $203.57   3.787%   $211.2792   $211.28   $211.30   $211.30  
  7 purchase totals = $1,114.59       $1,209.8421   $1,209.84   $1,209.90   $1,209.70