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 $60.81   4.844%   $63.7556   $63.76   $63.75   $63.80  
  Purchase #2 $212.89   8.259%   $230.4726   $230.47   $230.45   $230.50  
  Purchase #3 $181.64   3.566%   $188.1173   $188.12   $188.10   $188.10  
  Purchase #4 $52.45   6.513%   $55.8661   $55.87   $55.85   $55.90  
  Purchase #5 $226.48   5.316%   $238.5197   $238.52   $238.50   $238.50  
  Purchase #6 $29.50   6.280%   $31.3526   $31.35   $31.35   $31.40  
  Purchase #7 $55.78   8.393%   $60.4616   $60.46   $60.45   $60.50  
  7 purchase totals = $819.55       $868.5455   $868.55   $868.45   $868.70