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 $166.28   11.167%   $184.8485   $184.85   $184.85   $184.80  
  Purchase #2 $23.84   10.203%   $26.2724   $26.27   $26.25   $26.30  
  Purchase #3 $146.26   6.202%   $155.331   $155.33   $155.35   $155.30  
  Purchase #4 $126.57   12.863%   $142.8507   $142.85   $142.85   $142.90  
  Purchase #5 $194.50   6.790%   $207.7066   $207.71   $207.70   $207.70  
  Purchase #6 $213.29   13.219%   $241.4848   $241.48   $241.50   $241.50  
  Purchase #7 $54.48   12.603%   $61.3461   $61.35   $61.35   $61.30  
  7 purchase totals = $925.22       $1,019.8401   $1,019.84   $1,019.85   $1,019.80