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 $219.41   10.708%   $242.9044   $242.90   $242.90   $242.90  
  Purchase #2 $157.41   3.363%   $162.7037   $162.70   $162.70   $162.70  
  Purchase #3 $147.42   12.608%   $166.0067   $166.01   $166.00   $166.00  
  Purchase #4 $118.66   4.627%   $124.1504   $124.15   $124.15   $124.20  
  Purchase #5 $189.85   13.189%   $214.8893   $214.89   $214.90   $214.90  
  Purchase #6 $219.74   10.815%   $243.5049   $243.50   $243.50   $243.50  
  Purchase #7 $68.97   9.427%   $75.4718   $75.47   $75.45   $75.50  
  7 purchase totals = $1,121.46       $1,229.6312   $1,229.62   $1,229.60   $1,229.70