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 $98.41   8.251%   $106.5298   $106.53   $106.55   $106.50  
  Purchase #2 $130.40   12.598%   $146.8278   $146.83   $146.85   $146.80  
  Purchase #3 $177.82   13.241%   $201.3651   $201.37   $201.35   $201.40  
  Purchase #4 $225.90   12.239%   $253.5479   $253.55   $253.55   $253.50  
  Purchase #5 $173.25   3.674%   $179.6152   $179.62   $179.60   $179.60  
  Purchase #6 $93.74   9.293%   $102.4513   $102.45   $102.45   $102.50  
  Purchase #7 $59.89   8.315%   $64.8699   $64.87   $64.85   $64.90  
  7 purchase totals = $959.41       $1,055.2070   $1,055.22   $1,055.20   $1,055.20