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 $240.37   10.213%   $264.919   $264.92   $264.90   $264.90  
  Purchase #2 $25.97   13.832%   $29.5622   $29.56   $29.55   $29.60  
  Purchase #3 $222.42   5.239%   $234.0726   $234.07   $234.05   $234.10  
  Purchase #4 $46.49   3.164%   $47.9609   $47.96   $47.95   $48.00  
  Purchase #5 $161.78   3.735%   $167.8225   $167.82   $167.80   $167.80  
  Purchase #6 $71.74   8.556%   $77.8781   $77.88   $77.90   $77.90  
  Purchase #7 $219.25   10.148%   $241.4995   $241.50   $241.50   $241.50  
  7 purchase totals = $988.02       $1,063.7148   $1,063.71   $1,063.65   $1,063.80