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 $211.25   11.727%   $236.0233   $236.02   $236.00   $236.00  
  Purchase #2 $30.97   4.245%   $32.2847   $32.28   $32.30   $32.30  
  Purchase #3 $216.69   5.724%   $229.0933   $229.09   $229.10   $229.10  
  Purchase #4 $144.81   5.374%   $152.5921   $152.59   $152.60   $152.60  
  Purchase #5 $100.52   7.249%   $107.8067   $107.81   $107.80   $107.80  
  Purchase #6 $79.65   7.376%   $85.525   $85.53   $85.55   $85.50  
  Purchase #7 $166.51   8.389%   $180.4785   $180.48   $180.50   $180.50  
  7 purchase totals = $950.40       $1,023.8036   $1,023.80   $1,023.85   $1,023.80