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 $165.27   11.761%   $184.7074   $184.71   $184.70   $184.70  
  Purchase #2 $230.76   13.815%   $262.6395   $262.64   $262.65   $262.60  
  Purchase #3 $138.44   5.300%   $145.7773   $145.78   $145.80   $145.80  
  Purchase #4 $141.98   12.225%   $159.3371   $159.34   $159.35   $159.30  
  Purchase #5 $32.75   8.165%   $35.424   $35.42   $35.40   $35.40  
  Purchase #6 $231.78   4.786%   $242.873   $242.87   $242.85   $242.90  
  Purchase #7 $132.61   4.472%   $138.5403   $138.54   $138.55   $138.50  
  7 purchase totals = $1,073.59       $1,169.2986   $1,169.30   $1,169.30   $1,169.20