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 $68.62   7.785%   $73.9621   $73.96   $73.95   $74.00  
  Purchase #2 $226.59   12.196%   $254.2249   $254.22   $254.20   $254.20  
  Purchase #3 $115.95   13.434%   $131.5267   $131.53   $131.55   $131.50  
  Purchase #4 $17.95   4.789%   $18.8096   $18.81   $18.80   $18.80  
  Purchase #5 $115.65   4.364%   $120.697   $120.70   $120.70   $120.70  
  Purchase #6 $70.60   12.508%   $79.4306   $79.43   $79.45   $79.40  
  Purchase #7 $112.74   8.196%   $121.9802   $121.98   $122.00   $122.00  
  7 purchase totals = $728.10       $800.6311   $800.63   $800.65   $800.60