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 $61.93   12.219%   $69.4972   $69.50   $69.50   $69.50  
  Purchase #2 $196.84   13.760%   $223.9252   $223.93   $223.95   $223.90  
  Purchase #3 $142.41   10.759%   $157.7319   $157.73   $157.75   $157.70  
  Purchase #4 $200.76   5.316%   $211.4324   $211.43   $211.45   $211.40  
  Purchase #5 $68.91   3.179%   $71.1006   $71.10   $71.10   $71.10  
  Purchase #6 $81.60   10.546%   $90.2055   $90.21   $90.20   $90.20  
  Purchase #7 $193.26   9.285%   $211.2042   $211.20   $211.20   $211.20  
  7 purchase totals = $945.71       $1,035.0970   $1,035.10   $1,035.15   $1,035.00