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 $91.91   5.256%   $96.7408   $96.74   $96.75   $96.70  
  Purchase #2 $157.95   9.804%   $173.4354   $173.44   $173.45   $173.40  
  Purchase #3 $72.77   8.127%   $78.684   $78.68   $78.70   $78.70  
  Purchase #4 $216.50   7.508%   $232.7548   $232.75   $232.75   $232.80  
  Purchase #5 $82.31   12.323%   $92.4531   $92.45   $92.45   $92.50  
  Purchase #6 $189.73   9.155%   $207.0998   $207.10   $207.10   $207.10  
  Purchase #7 $168.90   8.373%   $183.042   $183.04   $183.05   $183.00  
  7 purchase totals = $980.07       $1,064.2099   $1,064.20   $1,064.25   $1,064.20