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 $59.72   5.431%   $62.9634   $62.96   $62.95   $63.00  
  Purchase #2 $46.53   5.314%   $49.0026   $49.00   $49.00   $49.00  
  Purchase #3 $147.75   5.145%   $155.3517   $155.35   $155.35   $155.40  
  Purchase #4 $77.72   6.369%   $82.67   $82.67   $82.65   $82.70  
  Purchase #5 $206.91   4.425%   $216.0658   $216.07   $216.05   $216.10  
  Purchase #6 $120.31   3.833%   $124.9215   $124.92   $124.90   $124.90  
  Purchase #7 $79.33   5.483%   $83.6797   $83.68   $83.70   $83.70  
  7 purchase totals = $738.27       $774.6547   $774.65   $774.60   $774.80