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 $211.45   3.363%   $218.5611   $218.56   $218.55   $218.60  
  Purchase #2 $92.33   11.106%   $102.5842   $102.58   $102.60   $102.60  
  Purchase #3 $84.76   7.632%   $91.2289   $91.23   $91.25   $91.20  
  Purchase #4 $156.68   6.442%   $166.7733   $166.77   $166.75   $166.80  
  Purchase #5 $81.43   11.600%   $90.8759   $90.88   $90.90   $90.90  
  Purchase #6 $187.78   3.430%   $194.2209   $194.22   $194.20   $194.20  
  Purchase #7 $43.41   13.581%   $49.3055   $49.31   $49.30   $49.30  
  7 purchase totals = $857.84       $913.5498   $913.55   $913.55   $913.60