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 $86.59   9.552%   $94.8611   $94.86   $94.85   $94.90  
  Purchase #2 $153.82   12.471%   $173.0029   $173.00   $173.00   $173.00  
  Purchase #3 $146.65   4.135%   $152.714   $152.71   $152.70   $152.70  
  Purchase #4 $227.28   10.737%   $251.6831   $251.68   $251.70   $251.70  
  Purchase #5 $192.51   4.532%   $201.2346   $201.23   $201.25   $201.20  
  Purchase #6 $22.25   9.777%   $24.4254   $24.43   $24.45   $24.40  
  Purchase #7 $98.84   6.612%   $105.3753   $105.38   $105.40   $105.40  
  7 purchase totals = $927.94       $1,003.2964   $1,003.29   $1,003.35   $1,003.30