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 $53.99   5.179%   $56.7861   $56.79   $56.80   $56.80  
  Purchase #2 $191.51   5.392%   $201.8362   $201.84   $201.85   $201.80  
  Purchase #3 $218.43   9.348%   $238.8488   $238.85   $238.85   $238.80  
  Purchase #4 $185.76   12.376%   $208.7497   $208.75   $208.75   $208.70  
  Purchase #5 $96.74   8.481%   $104.9445   $104.94   $104.95   $104.90  
  Purchase #6 $24.91   6.135%   $26.4382   $26.44   $26.45   $26.40  
  Purchase #7 $176.62   6.649%   $188.3635   $188.36   $188.35   $188.40  
  7 purchase totals = $947.96       $1,025.9670   $1,025.97   $1,026.00   $1,025.80