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 $44.35   12.207%   $49.7638   $49.76   $49.75   $49.80  
  Purchase #2 $189.73   9.769%   $208.2647   $208.26   $208.25   $208.30  
  Purchase #3 $73.75   5.583%   $77.8675   $77.87   $77.85   $77.90  
  Purchase #4 $32.50   4.854%   $34.0776   $34.08   $34.10   $34.10  
  Purchase #5 $177.44   13.810%   $201.9445   $201.94   $201.95   $201.90  
  Purchase #6 $57.60   6.361%   $61.2639   $61.26   $61.25   $61.30  
  Purchase #7 $127.82   4.818%   $133.9784   $133.98   $134.00   $134.00  
  7 purchase totals = $703.19       $767.1604   $767.15   $767.15   $767.30