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 $123.57   8.360%   $133.9005   $133.90   $133.90   $133.90  
  Purchase #2 $179.39   7.570%   $192.9698   $192.97   $192.95   $193.00  
  Purchase #3 $46.89   12.743%   $52.8652   $52.87   $52.85   $52.90  
  Purchase #4 $183.44   12.156%   $205.739   $205.74   $205.75   $205.70  
  Purchase #5 $68.54   13.583%   $77.8498   $77.85   $77.85   $77.80  
  Purchase #6 $162.41   9.830%   $178.3749   $178.37   $178.35   $178.40  
  Purchase #7 $165.77   10.363%   $182.9487   $182.95   $182.95   $182.90  
  7 purchase totals = $930.01       $1,024.6479   $1,024.65   $1,024.60   $1,024.60