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 $68.47   7.415%   $73.5471   $73.55   $73.55   $73.50  
  Purchase #2 $16.97   4.295%   $17.6989   $17.70   $17.70   $17.70  
  Purchase #3 $63.54   5.600%   $67.0982   $67.10   $67.10   $67.10  
  Purchase #4 $18.94   13.721%   $21.5388   $21.54   $21.55   $21.50  
  Purchase #5 $216.37   3.726%   $224.4319   $224.43   $224.45   $224.40  
  Purchase #6 $225.70   4.672%   $236.2447   $236.24   $236.25   $236.20  
  Purchase #7 $175.52   6.245%   $186.4812   $186.48   $186.50   $186.50  
  7 purchase totals = $785.51       $827.0408   $827.04   $827.10   $826.90