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 $185.66   11.542%   $207.0889   $207.09   $207.10   $207.10  
  Purchase #2 $228.67   12.127%   $256.4008   $256.40   $256.40   $256.40  
  Purchase #3 $81.94   11.830%   $91.6335   $91.63   $91.65   $91.60  
  Purchase #4 $158.83   11.201%   $176.6205   $176.62   $176.60   $176.60  
  Purchase #5 $143.32   9.424%   $156.8265   $156.83   $156.85   $156.80  
  Purchase #6 $143.63   13.255%   $162.6682   $162.67   $162.65   $162.70  
  Purchase #7 $121.38   7.346%   $130.2966   $130.30   $130.30   $130.30  
  7 purchase totals = $1,063.43       $1,181.5350   $1,181.54   $1,181.55   $1,181.50