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 $60.33   10.142%   $66.4487   $66.45   $66.45   $66.40  
  Purchase #2 $250.43   10.395%   $276.4622   $276.46   $276.45   $276.50  
  Purchase #3 $45.37   10.152%   $49.976   $49.98   $50.00   $50.00  
  Purchase #4 $118.90   13.234%   $134.6352   $134.64   $134.65   $134.60  
  Purchase #5 $118.98   6.485%   $126.6959   $126.70   $126.70   $126.70  
  Purchase #6 $52.42   9.787%   $57.5503   $57.55   $57.55   $57.60  
  Purchase #7 $234.46   9.788%   $257.4089   $257.41   $257.40   $257.40  
  7 purchase totals = $880.89       $969.1772   $969.19   $969.20   $969.20