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 $62.87   8.668%   $68.3196   $68.32   $68.30   $68.30  
  Purchase #2 $217.94   8.230%   $235.8765   $235.88   $235.90   $235.90  
  Purchase #3 $224.60   8.451%   $243.5809   $243.58   $243.60   $243.60  
  Purchase #4 $50.92   8.499%   $55.2477   $55.25   $55.25   $55.20  
  Purchase #5 $245.79   7.573%   $264.4037   $264.40   $264.40   $264.40  
  Purchase #6 $20.51   11.384%   $22.8449   $22.84   $22.85   $22.80  
  Purchase #7 $248.71   5.617%   $262.68   $262.68   $262.70   $262.70  
  7 purchase totals = $1,071.34       $1,152.9533   $1,152.95   $1,153.00   $1,152.90