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 $54.98   3.443%   $56.873   $56.87   $56.85   $56.90  
  Purchase #2 $168.66   7.639%   $181.5439   $181.54   $181.55   $181.50  
  Purchase #3 $69.79   8.237%   $75.5386   $75.54   $75.55   $75.50  
  Purchase #4 $189.51   12.746%   $213.6649   $213.66   $213.65   $213.70  
  Purchase #5 $226.87   12.490%   $255.2061   $255.21   $255.20   $255.20  
  Purchase #6 $53.90   5.218%   $56.7125   $56.71   $56.70   $56.70  
  Purchase #7 $80.93   11.860%   $90.5283   $90.53   $90.55   $90.50  
  7 purchase totals = $844.64       $930.0673   $930.06   $930.05   $930.00