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 $56.97   9.150%   $62.1828   $62.18   $62.20   $62.20  
  Purchase #2 $219.34   5.280%   $230.9212   $230.92   $230.90   $230.90  
  Purchase #3 $62.36   11.169%   $69.325   $69.33   $69.35   $69.30  
  Purchase #4 $179.75   6.182%   $190.8621   $190.86   $190.85   $190.90  
  Purchase #5 $132.74   3.253%   $137.058   $137.06   $137.05   $137.10  
  Purchase #6 $157.77   8.633%   $171.3903   $171.39   $171.40   $171.40  
  Purchase #7 $161.81   6.523%   $172.3649   $172.36   $172.35   $172.40  
  7 purchase totals = $970.74       $1,034.1043   $1,034.10   $1,034.10   $1,034.20