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 $46.25   9.866%   $50.813   $50.81   $50.80   $50.80  
  Purchase #2 $215.86   4.792%   $226.204   $226.20   $226.20   $226.20  
  Purchase #3 $147.45   11.690%   $164.6869   $164.69   $164.70   $164.70  
  Purchase #4 $247.94   9.765%   $272.1513   $272.15   $272.15   $272.20  
  Purchase #5 $219.97   11.619%   $245.5283   $245.53   $245.55   $245.50  
  Purchase #6 $202.85   7.320%   $217.6986   $217.70   $217.70   $217.70  
  Purchase #7 $66.88   12.221%   $75.0534   $75.05   $75.05   $75.10  
  7 purchase totals = $1,147.20       $1,252.1355   $1,252.13   $1,252.15   $1,252.20