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 $93.63   3.112%   $96.5438   $96.54   $96.55   $96.50  
  Purchase #2 $44.57   11.821%   $49.8386   $49.84   $49.85   $49.80  
  Purchase #3 $119.59   12.665%   $134.7361   $134.74   $134.75   $134.70  
  Purchase #4 $165.28   13.623%   $187.7961   $187.80   $187.80   $187.80  
  Purchase #5 $242.91   13.152%   $274.8575   $274.86   $274.85   $274.90  
  Purchase #6 $182.74   4.780%   $191.475   $191.48   $191.50   $191.50  
  Purchase #7 $111.71   7.784%   $120.4055   $120.41   $120.40   $120.40  
  7 purchase totals = $960.43       $1,055.6526   $1,055.67   $1,055.70   $1,055.60