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 $196.68   10.270%   $216.879   $216.88   $216.90   $216.90  
  Purchase #2 $190.70   7.775%   $205.5269   $205.53   $205.55   $205.50  
  Purchase #3 $70.41   6.416%   $74.9275   $74.93   $74.95   $74.90  
  Purchase #4 $179.79   12.319%   $201.9383   $201.94   $201.95   $201.90  
  Purchase #5 $72.94   4.596%   $76.2923   $76.29   $76.30   $76.30  
  Purchase #6 $159.85   12.466%   $179.7769   $179.78   $179.80   $179.80  
  Purchase #7 $61.51   3.412%   $63.6087   $63.61   $63.60   $63.60  
  7 purchase totals = $931.88       $1,018.9496   $1,018.96   $1,019.05   $1,018.90