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 $167.83   9.580%   $183.9081   $183.91   $183.90   $183.90  
  Purchase #2 $111.99   7.776%   $120.6983   $120.70   $120.70   $120.70  
  Purchase #3 $201.94   6.161%   $214.3815   $214.38   $214.40   $214.40  
  Purchase #4 $80.44   4.692%   $84.2142   $84.21   $84.20   $84.20  
  Purchase #5 $208.81   4.533%   $218.2754   $218.28   $218.30   $218.30  
  Purchase #6 $57.82   6.341%   $61.4864   $61.49   $61.50   $61.50  
  Purchase #7 $197.29   6.444%   $210.0034   $210.00   $210.00   $210.00  
  7 purchase totals = $1,026.12       $1,092.9673   $1,092.97   $1,093.00   $1,093.00