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 $223.63   13.222%   $253.1984   $253.20   $253.20   $253.20  
  Purchase #2 $65.83   11.581%   $73.4538   $73.45   $73.45   $73.50  
  Purchase #3 $165.34   9.594%   $181.2027   $181.20   $181.20   $181.20  
  Purchase #4 $201.65   8.588%   $218.9677   $218.97   $218.95   $219.00  
  Purchase #5 $142.96   13.783%   $162.6642   $162.66   $162.65   $162.70  
  Purchase #6 $212.92   5.642%   $224.9329   $224.93   $224.95   $224.90  
  Purchase #7 $221.75   6.790%   $236.8068   $236.81   $236.80   $236.80  
  7 purchase totals = $1,234.08       $1,351.2265   $1,351.22   $1,351.20   $1,351.30