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 $175.45   5.163%   $184.5085   $184.51   $184.50   $184.50  
  Purchase #2 $236.81   8.842%   $257.7487   $257.75   $257.75   $257.70  
  Purchase #3 $172.45   4.196%   $179.686   $179.69   $179.70   $179.70  
  Purchase #4 $202.79   7.463%   $217.9242   $217.92   $217.90   $217.90  
  Purchase #5 $62.28   11.784%   $69.6191   $69.62   $69.60   $69.60  
  Purchase #6 $141.57   7.785%   $152.5912   $152.59   $152.60   $152.60  
  Purchase #7 $151.84   12.122%   $170.246   $170.25   $170.25   $170.20  
  7 purchase totals = $1,143.19       $1,232.3237   $1,232.33   $1,232.30   $1,232.20