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 $14.86   8.518%   $16.1258   $16.13   $16.15   $16.10  
  Purchase #2 $104.77   3.206%   $108.1289   $108.13   $108.15   $108.10  
  Purchase #3 $203.44   6.301%   $216.2588   $216.26   $216.25   $216.30  
  Purchase #4 $148.33   4.731%   $155.3475   $155.35   $155.35   $155.30  
  Purchase #5 $67.30   9.804%   $73.8981   $73.90   $73.90   $73.90  
  Purchase #6 $130.35   3.539%   $134.9631   $134.96   $134.95   $135.00  
  Purchase #7 $80.82   13.222%   $91.506   $91.51   $91.50   $91.50  
  7 purchase totals = $749.87       $796.2282   $796.24   $796.25   $796.20