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 $70.71   11.511%   $78.8494   $78.85   $78.85   $78.80  
  Purchase #2 $220.84   9.335%   $241.4554   $241.46   $241.45   $241.50  
  Purchase #3 $73.70   10.107%   $81.1489   $81.15   $81.15   $81.10  
  Purchase #4 $136.58   6.367%   $145.276   $145.28   $145.30   $145.30  
  Purchase #5 $187.55   4.214%   $195.4534   $195.45   $195.45   $195.50  
  Purchase #6 $84.53   10.317%   $93.251   $93.25   $93.25   $93.30  
  Purchase #7 $224.51   3.199%   $231.6921   $231.69   $231.70   $231.70  
  7 purchase totals = $998.42       $1,067.1262   $1,067.13   $1,067.15   $1,067.20