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 $54.55   5.749%   $57.6861   $57.69   $57.70   $57.70  
  Purchase #2 $120.55   11.872%   $134.8617   $134.86   $134.85   $134.90  
  Purchase #3 $241.66   6.475%   $257.3075   $257.31   $257.30   $257.30  
  Purchase #4 $152.68   6.450%   $162.5279   $162.53   $162.55   $162.50  
  Purchase #5 $154.33   7.344%   $165.664   $165.66   $165.65   $165.70  
  Purchase #6 $219.99   12.398%   $247.2644   $247.26   $247.25   $247.30  
  Purchase #7 $119.50   9.275%   $130.5836   $130.58   $130.60   $130.60  
  7 purchase totals = $1,063.26       $1,155.8952   $1,155.89   $1,155.90   $1,156.00