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 $35.79   7.747%   $38.5627   $38.56   $38.55   $38.60  
  Purchase #2 $155.52   12.238%   $174.5525   $174.55   $174.55   $174.60  
  Purchase #3 $245.55   7.541%   $264.0669   $264.07   $264.05   $264.10  
  Purchase #4 $118.91   3.544%   $123.1242   $123.12   $123.10   $123.10  
  Purchase #5 $101.51   11.658%   $113.344   $113.34   $113.35   $113.30  
  Purchase #6 $73.81   5.536%   $77.8961   $77.90   $77.90   $77.90  
  Purchase #7 $87.88   3.541%   $90.9918   $90.99   $91.00   $91.00  
  7 purchase totals = $818.97       $882.5382   $882.53   $882.50   $882.60