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 $17.35   13.194%   $19.6392   $19.64   $19.65   $19.60  
  Purchase #2 $48.58   9.489%   $53.1898   $53.19   $53.20   $53.20  
  Purchase #3 $133.91   3.517%   $138.6196   $138.62   $138.60   $138.60  
  Purchase #4 $86.46   6.229%   $91.8456   $91.85   $91.85   $91.80  
  Purchase #5 $224.31   12.246%   $251.779   $251.78   $251.80   $251.80  
  Purchase #6 $205.55   5.476%   $216.8059   $216.81   $216.80   $216.80  
  Purchase #7 $66.47   12.370%   $74.6923   $74.69   $74.70   $74.70  
  7 purchase totals = $782.63       $846.5714   $846.58   $846.60   $846.50