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 $202.74   13.583%   $230.2782   $230.28   $230.30   $230.30  
  Purchase #2 $126.86   13.853%   $144.4339   $144.43   $144.45   $144.40  
  Purchase #3 $168.39   6.615%   $179.529   $179.53   $179.55   $179.50  
  Purchase #4 $49.87   12.850%   $56.2783   $56.28   $56.30   $56.30  
  Purchase #5 $215.93   13.534%   $245.154   $245.15   $245.15   $245.20  
  Purchase #6 $116.50   12.337%   $130.8726   $130.87   $130.85   $130.90  
  Purchase #7 $178.74   13.500%   $202.8699   $202.87   $202.85   $202.90  
  7 purchase totals = $1,059.03       $1,189.4159   $1,189.41   $1,189.45   $1,189.50