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 $96.33   8.222%   $104.2503   $104.25   $104.25   $104.30  
  Purchase #2 $213.67   9.698%   $234.3917   $234.39   $234.40   $234.40  
  Purchase #3 $120.61   3.523%   $124.8591   $124.86   $124.85   $124.90  
  Purchase #4 $105.40   10.281%   $116.2362   $116.24   $116.25   $116.20  
  Purchase #5 $172.86   3.314%   $178.5886   $178.59   $178.60   $178.60  
  Purchase #6 $56.66   11.701%   $63.2898   $63.29   $63.30   $63.30  
  Purchase #7 $60.30   11.140%   $67.0174   $67.02   $67.00   $67.00  
  7 purchase totals = $825.83       $888.6331   $888.64   $888.65   $888.70