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 $216.96   8.823%   $236.1024   $236.10   $236.10   $236.10  
  Purchase #2 $147.48   5.748%   $155.9572   $155.96   $155.95   $156.00  
  Purchase #3 $17.45   7.407%   $18.7425   $18.74   $18.75   $18.70  
  Purchase #4 $119.45   3.448%   $123.5686   $123.57   $123.55   $123.60  
  Purchase #5 $205.81   11.751%   $229.9947   $229.99   $230.00   $230.00  
  Purchase #6 $188.92   11.211%   $210.0998   $210.10   $210.10   $210.10  
  Purchase #7 $44.45   3.736%   $46.1107   $46.11   $46.10   $46.10  
  7 purchase totals = $940.52       $1,020.5759   $1,020.57   $1,020.55   $1,020.60