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 $25.68   4.137%   $26.7424   $26.74   $26.75   $26.70  
  Purchase #2 $162.65   13.155%   $184.0466   $184.05   $184.05   $184.00  
  Purchase #3 $147.62   7.574%   $158.8007   $158.80   $158.80   $158.80  
  Purchase #4 $161.27   3.220%   $166.4629   $166.46   $166.45   $166.50  
  Purchase #5 $236.87   8.834%   $257.7951   $257.80   $257.80   $257.80  
  Purchase #6 $125.59   6.118%   $133.2736   $133.27   $133.25   $133.30  
  Purchase #7 $75.53   6.652%   $80.5543   $80.55   $80.55   $80.60  
  7 purchase totals = $935.21       $1,007.6756   $1,007.67   $1,007.65   $1,007.70