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 $146.45   8.240%   $158.5175   $158.52   $158.50   $158.50  
  Purchase #2 $217.92   10.624%   $241.0718   $241.07   $241.05   $241.10  
  Purchase #3 $11.55   10.819%   $12.7996   $12.80   $12.80   $12.80  
  Purchase #4 $34.83   13.652%   $39.585   $39.59   $39.60   $39.60  
  Purchase #5 $216.88   5.308%   $228.392   $228.39   $228.40   $228.40  
  Purchase #6 $26.25   4.633%   $27.4662   $27.47   $27.45   $27.50  
  Purchase #7 $20.60   9.533%   $22.5638   $22.56   $22.55   $22.60  
  7 purchase totals = $674.48       $730.3959   $730.40   $730.35   $730.50