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 $228.33   4.675%   $239.0044   $239.00   $239.00   $239.00  
  Purchase #2 $30.67   10.647%   $33.9354   $33.94   $33.95   $33.90  
  Purchase #3 $151.76   12.644%   $170.9485   $170.95   $170.95   $170.90  
  Purchase #4 $226.29   4.317%   $236.0589   $236.06   $236.05   $236.10  
  Purchase #5 $36.61   6.386%   $38.9479   $38.95   $38.95   $38.90  
  Purchase #6 $148.39   9.699%   $162.7823   $162.78   $162.80   $162.80  
  Purchase #7 $128.94   9.756%   $141.5194   $141.52   $141.50   $141.50  
  7 purchase totals = $950.99       $1,023.1968   $1,023.20   $1,023.20   $1,023.10