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 $88.76   5.318%   $93.4803   $93.48   $93.50   $93.50  
  Purchase #2 $130.84   3.148%   $134.9588   $134.96   $134.95   $135.00  
  Purchase #3 $149.35   3.545%   $154.6445   $154.64   $154.65   $154.60  
  Purchase #4 $139.49   9.705%   $153.0275   $153.03   $153.05   $153.00  
  Purchase #5 $128.36   10.339%   $141.6311   $141.63   $141.65   $141.60  
  Purchase #6 $29.62   9.157%   $32.3323   $32.33   $32.35   $32.30  
  Purchase #7 $32.47   5.346%   $34.2058   $34.21   $34.20   $34.20  
  7 purchase totals = $698.89       $744.2803   $744.28   $744.35   $744.20