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 $10.26   10.348%   $11.3217   $11.32   $11.30   $11.30  
  Purchase #2 $167.53   8.197%   $181.2624   $181.26   $181.25   $181.30  
  Purchase #3 $59.79   4.538%   $62.5033   $62.50   $62.50   $62.50  
  Purchase #4 $91.64   5.572%   $96.7462   $96.75   $96.75   $96.70  
  Purchase #5 $246.48   5.774%   $260.7118   $260.71   $260.70   $260.70  
  Purchase #6 $162.60   7.687%   $175.0991   $175.10   $175.10   $175.10  
  Purchase #7 $124.62   9.122%   $135.9878   $135.99   $136.00   $136.00  
  7 purchase totals = $862.92       $923.6323   $923.63   $923.60   $923.60