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 $59.36   3.372%   $61.3616   $61.36   $61.35   $61.40  
  Purchase #2 $29.66   12.642%   $33.4096   $33.41   $33.40   $33.40  
  Purchase #3 $100.95   4.467%   $105.4594   $105.46   $105.45   $105.50  
  Purchase #4 $113.94   5.533%   $120.2443   $120.24   $120.25   $120.20  
  Purchase #5 $216.53   4.702%   $226.7112   $226.71   $226.70   $226.70  
  Purchase #6 $26.25   5.697%   $27.7455   $27.75   $27.75   $27.70  
  Purchase #7 $227.80   12.394%   $256.0335   $256.03   $256.05   $256.00  
  7 purchase totals = $774.49       $830.9651   $830.96   $830.95   $830.90