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 $60.83   9.279%   $66.4744   $66.47   $66.45   $66.50  
  Purchase #2 $193.83   7.243%   $207.8691   $207.87   $207.85   $207.90  
  Purchase #3 $31.83   8.511%   $34.5391   $34.54   $34.55   $34.50  
  Purchase #4 $201.56   12.108%   $225.9649   $225.96   $225.95   $226.00  
  Purchase #5 $176.75   7.322%   $189.6916   $189.69   $189.70   $189.70  
  Purchase #6 $222.87   7.680%   $239.9864   $239.99   $240.00   $240.00  
  Purchase #7 $43.25   11.359%   $48.1628   $48.16   $48.15   $48.20  
  7 purchase totals = $930.92       $1,012.6883   $1,012.68   $1,012.65   $1,012.80