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 $141.93   8.102%   $153.4292   $153.43   $153.45   $153.40  
  Purchase #2 $219.58   6.261%   $233.3279   $233.33   $233.35   $233.30  
  Purchase #3 $179.32   7.400%   $192.5897   $192.59   $192.60   $192.60  
  Purchase #4 $236.80   7.443%   $254.425   $254.43   $254.45   $254.40  
  Purchase #5 $158.69   5.737%   $167.794   $167.79   $167.80   $167.80  
  Purchase #6 $90.85   11.815%   $101.5839   $101.58   $101.60   $101.60  
  Purchase #7 $92.33   12.725%   $104.079   $104.08   $104.10   $104.10  
  7 purchase totals = $1,119.50       $1,207.2287   $1,207.23   $1,207.35   $1,207.20