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 $90.44   3.373%   $93.4905   $93.49   $93.50   $93.50  
  Purchase #2 $10.42   10.810%   $11.5464   $11.55   $11.55   $11.50  
  Purchase #3 $58.89   13.533%   $66.8596   $66.86   $66.85   $66.90  
  Purchase #4 $215.49   5.304%   $226.9196   $226.92   $226.90   $226.90  
  Purchase #5 $159.66   3.474%   $165.2066   $165.21   $165.20   $165.20  
  Purchase #6 $206.59   5.538%   $218.031   $218.03   $218.05   $218.00  
  Purchase #7 $228.61   6.727%   $243.9886   $243.99   $244.00   $244.00  
  7 purchase totals = $970.10       $1,026.0423   $1,026.05   $1,026.05   $1,026.00