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 $55.92   8.730%   $60.8018   $60.80   $60.80   $60.80  
  Purchase #2 $184.52   13.168%   $208.8176   $208.82   $208.80   $208.80  
  Purchase #3 $98.96   6.403%   $105.2964   $105.30   $105.30   $105.30  
  Purchase #4 $89.85   4.173%   $93.5994   $93.60   $93.60   $93.60  
  Purchase #5 $214.64   12.575%   $241.631   $241.63   $241.65   $241.60  
  Purchase #6 $26.97   7.513%   $28.9963   $29.00   $29.00   $29.00  
  Purchase #7 $23.99   7.753%   $25.8499   $25.85   $25.85   $25.80  
  7 purchase totals = $694.85       $764.9924   $765.00   $765.00   $764.90