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 $161.49   11.217%   $179.6043   $179.60   $179.60   $179.60  
  Purchase #2 $205.59   11.135%   $228.4824   $228.48   $228.50   $228.50  
  Purchase #3 $44.66   10.730%   $49.452   $49.45   $49.45   $49.50  
  Purchase #4 $206.70   6.265%   $219.6498   $219.65   $219.65   $219.60  
  Purchase #5 $213.90   10.733%   $236.8579   $236.86   $236.85   $236.90  
  Purchase #6 $38.41   10.871%   $42.5856   $42.59   $42.60   $42.60  
  Purchase #7 $195.95   11.740%   $218.9545   $218.95   $218.95   $219.00  
  7 purchase totals = $1,066.70       $1,175.5865   $1,175.58   $1,175.60   $1,175.70