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 $60.88   9.629%   $66.7421   $66.74   $66.75   $66.70  
  Purchase #2 $82.67   8.450%   $89.6556   $89.66   $89.65   $89.70  
  Purchase #3 $154.51   3.183%   $159.4281   $159.43   $159.45   $159.40  
  Purchase #4 $234.27   5.297%   $246.6793   $246.68   $246.70   $246.70  
  Purchase #5 $199.86   3.724%   $207.3028   $207.30   $207.30   $207.30  
  Purchase #6 $166.56   10.829%   $184.5968   $184.60   $184.60   $184.60  
  Purchase #7 $146.80   6.115%   $155.7768   $155.78   $155.80   $155.80  
  7 purchase totals = $1,045.55       $1,110.1815   $1,110.19   $1,110.25   $1,110.20