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 $123.92   11.162%   $137.752   $137.75   $137.75   $137.80  
  Purchase #2 $101.78   4.148%   $106.0018   $106.00   $106.00   $106.00  
  Purchase #3 $113.81   11.327%   $126.7013   $126.70   $126.70   $126.70  
  Purchase #4 $207.69   5.831%   $219.8004   $219.80   $219.80   $219.80  
  Purchase #5 $235.26   10.802%   $260.6728   $260.67   $260.65   $260.70  
  Purchase #6 $119.93   12.128%   $134.4751   $134.48   $134.50   $134.50  
  Purchase #7 $91.31   5.677%   $96.4937   $96.49   $96.50   $96.50  
  7 purchase totals = $993.70       $1,081.8971   $1,081.89   $1,081.90   $1,082.00