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 $59.80   10.202%   $65.9008   $65.90   $65.90   $65.90  
  Purchase #2 $225.94   5.723%   $238.8705   $238.87   $238.85   $238.90  
  Purchase #3 $250.57   6.789%   $267.5812   $267.58   $267.60   $267.60  
  Purchase #4 $163.95   8.327%   $177.6021   $177.60   $177.60   $177.60  
  Purchase #5 $15.49   9.251%   $16.923   $16.92   $16.90   $16.90  
  Purchase #6 $53.90   9.502%   $59.0216   $59.02   $59.00   $59.00  
  Purchase #7 $166.96   7.788%   $179.9628   $179.96   $179.95   $180.00  
  7 purchase totals = $936.61       $1,005.8620   $1,005.85   $1,005.80   $1,005.90