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 $244.30   6.552%   $260.3065   $260.31   $260.30   $260.30  
  Purchase #2 $114.33   6.641%   $121.9227   $121.92   $121.90   $121.90  
  Purchase #3 $139.96   8.696%   $152.1309   $152.13   $152.15   $152.10  
  Purchase #4 $182.68   10.409%   $201.6952   $201.70   $201.70   $201.70  
  Purchase #5 $232.91   8.127%   $251.8386   $251.84   $251.85   $251.80  
  Purchase #6 $15.52   6.489%   $16.5271   $16.53   $16.55   $16.50  
  Purchase #7 $55.59   13.438%   $63.0602   $63.06   $63.05   $63.10  
  7 purchase totals = $985.29       $1,067.4812   $1,067.49   $1,067.50   $1,067.40