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 $197.77   10.763%   $219.056   $219.06   $219.05   $219.10  
  Purchase #2 $6.26   9.118%   $6.8308   $6.83   $6.85   $6.80  
  Purchase #3 $164.71   13.272%   $186.5703   $186.57   $186.55   $186.60  
  Purchase #4 $250.28   5.109%   $263.0668   $263.07   $263.05   $263.10  
  Purchase #5 $12.94   9.753%   $14.202   $14.20   $14.20   $14.20  
  Purchase #6 $175.65   9.337%   $192.0504   $192.05   $192.05   $192.10  
  Purchase #7 $50.31   10.422%   $55.5533   $55.55   $55.55   $55.60  
  7 purchase totals = $857.92       $937.3296   $937.33   $937.30   $937.50