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 $228.62   5.573%   $241.361   $241.36   $241.35   $241.40  
  Purchase #2 $105.82   13.761%   $120.3819   $120.38   $120.40   $120.40  
  Purchase #3 $61.40   7.685%   $66.1186   $66.12   $66.10   $66.10  
  Purchase #4 $155.89   7.114%   $166.98   $166.98   $167.00   $167.00  
  Purchase #5 $5.60   10.623%   $6.1949   $6.19   $6.20   $6.20  
  Purchase #6 $188.76   5.795%   $199.6986   $199.70   $199.70   $199.70  
  Purchase #7 $23.46   12.791%   $26.4608   $26.46   $26.45   $26.50  
  7 purchase totals = $769.55       $827.1958   $827.19   $827.20   $827.30