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 $153.57   9.619%   $168.3419   $168.34   $168.35   $168.30  
  Purchase #2 $187.43   7.539%   $201.5603   $201.56   $201.55   $201.60  
  Purchase #3 $198.94   12.277%   $223.3639   $223.36   $223.35   $223.40  
  Purchase #4 $87.98   8.561%   $95.512   $95.51   $95.50   $95.50  
  Purchase #5 $38.45   6.177%   $40.8251   $40.83   $40.85   $40.80  
  Purchase #6 $46.68   8.841%   $50.807   $50.81   $50.80   $50.80  
  Purchase #7 $28.58   6.750%   $30.5092   $30.51   $30.50   $30.50  
  7 purchase totals = $741.63       $810.9194   $810.92   $810.90   $810.90