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 $190.57   8.422%   $206.6198   $206.62   $206.60   $206.60  
  Purchase #2 $96.47   11.494%   $107.5583   $107.56   $107.55   $107.60  
  Purchase #3 $90.36   12.121%   $101.3125   $101.31   $101.30   $101.30  
  Purchase #4 $109.71   8.797%   $119.3612   $119.36   $119.35   $119.40  
  Purchase #5 $206.58   7.241%   $221.5385   $221.54   $221.55   $221.50  
  Purchase #6 $96.85   13.774%   $110.1901   $110.19   $110.20   $110.20  
  Purchase #7 $173.78   7.433%   $186.6971   $186.70   $186.70   $186.70  
  7 purchase totals = $964.32       $1,053.2775   $1,053.28   $1,053.25   $1,053.30