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 $40.76   7.179%   $43.6862   $43.69   $43.70   $43.70  
  Purchase #2 $132.41   6.451%   $140.9518   $140.95   $140.95   $141.00  
  Purchase #3 $61.44   5.825%   $65.0189   $65.02   $65.00   $65.00  
  Purchase #4 $192.73   8.850%   $209.7866   $209.79   $209.80   $209.80  
  Purchase #5 $206.38   8.639%   $224.2092   $224.21   $224.20   $224.20  
  Purchase #6 $159.98   8.531%   $173.6279   $173.63   $173.65   $173.60  
  Purchase #7 $235.69   6.827%   $251.7806   $251.78   $251.80   $251.80  
  7 purchase totals = $1,029.39       $1,109.0612   $1,109.07   $1,109.10   $1,109.10