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 $82.35   4.318%   $85.9059   $85.91   $85.90   $85.90  
  Purchase #2 $201.37   12.181%   $225.8989   $225.90   $225.90   $225.90  
  Purchase #3 $14.81   4.320%   $15.4498   $15.45   $15.45   $15.40  
  Purchase #4 $226.93   10.842%   $251.5338   $251.53   $251.55   $251.50  
  Purchase #5 $203.53   12.186%   $228.3322   $228.33   $228.35   $228.30  
  Purchase #6 $192.42   7.168%   $206.2127   $206.21   $206.20   $206.20  
  Purchase #7 $98.56   8.192%   $106.634   $106.63   $106.65   $106.60  
  7 purchase totals = $1,019.97       $1,119.9673   $1,119.96   $1,120.00   $1,119.80